Gallery: British royals at subway station, zoo

Britain's Kate, the Duchess of Cambridge, reacts as she is presented a badge that says "Baby on Board", normally available to pregnant passengers to encourage others to give them a seat, watched by Britain's Queen Elizabeth II, bottom, at Baker Street underground station in London, for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Kate the Duchess of Cambridge receives flowers from a little girl at the 1st Battalion Irish Guards' St Patrick's Day Parade at Mons Barracks in Aldershot, England, Sunday, March 17, 2013. Kate presenting the sprigs of shamrocks to the regiment Sunday, follows a century-old tradition inaugurated by Queen Alexandra, the wife of the then King, Edward VII back in 1901. (AP Photo/Matt Dunham)

Britain's Queen Elizabeth II is shown round the carriage of a parked train at Baker Street underground station in London, for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Chris Radburn, Pool)

Britain's Queen Elizabeth II walks down stairs as she visits Baker Street underground station in London, to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Kate, the Duchess of Cambridge watches after Britain's Elizabeth II unveiled a plaque at Baker Street underground station in London, to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Kate, the Duchess of Cambridge walks across a platform as she visits Baker Street underground station in London, to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Kate, the Duchess of Cambridge, center, is backdropped by the carriage of a vintage train at Baker Street underground station in London, for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. Britain's Queen Elizabeth II made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Kate, Duchess of Cambridge, holds a badge that reads "Baby on Board", as she accompanies Queen Elizabeth II and Prince Philip, not pictured, at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Chris Radburn, Pool)

Britain's Kate, Duchess of Cambridge, accompanies Queen Elizabeth II and Prince Philip, not pictured, arrives at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Chris Radburn, Pool)

Britain's Kate, the Duchess of Cambridge, passes through a ticket barrier at Baker Street underground station in London, for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Chris Radburn, Pool)

Britain's Queen Elizabeth II walks across a platform as she visits Baker Street underground station in London, to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Queen Elizabeth II smiles as she visits Baker Street underground station in London, to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Kate, the Duchess of Cambridge, speaks to someone at Baker Street underground station in London, for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. Britain's Queen Elizabeth II made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Queen Elizabeth II walks through the carriage of a parked train she was shown around at Baker Street underground station in London, for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Kate, the Duchess of Cambridge, speaks to someone at Baker Street underground station in London, for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. Britain's Queen Elizabeth II made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Queen Elizabeth II leaves Baker Street underground station in London after a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, the Duchess of Cambridge, watches as Britain's Queen Elizabeth II unveils a plaque at Baker Street underground station in London, during a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Kate, Duchess of Cambridge, right, accompanies Queen Elizabeth II, unssen, and Prince Philip, left, arrives at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, Duchess of Cambridge accompanies Queen Elizabeth II and Prince Philip, unseen, leaves Baker Street underground station in London after a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Queen Elizabeth II steps off a parked train she was shown around at Baker Street underground station in London, for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate Duchess of Cambridge, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Matt Dunham)

Britain's Kate, Duchess of Cambridge, accompanies Queen Elizabeth II and Prince Philip, not pictured, leaves Baker Street underground station in London after a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, Duchess of Cambridge, right, accompanies Queen Elizabeth II, unseen, and Prince Philip, left, at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, Duchess of Cambridge, accompanies Queen Elizabeth II and Prince Philip, not pictured, arrives at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, Duchess of Cambridge, accompanies Queen Elizabeth II and Prince Philip, not pictured, arrives at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, Duchess of Cambridge, accompanies Queen Elizabeth II and Prince Philip, not pictured, arrives at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, Duchess of Cambridge, accompanies Queen Elizabeth II and Prince Philip, not pictured, arrives at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, Duchess of Cambridge, right, accompanies Queen Elizabeth II, left, and Prince Philip, center, as they arrive at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, Duchess of Cambridge, right, accompanies Queen Elizabeth II and Prince Philip, third left and fourth, arrives at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Kate, Duchess of Cambridge, right, accompanies Queen Elizabeth II and Prince Philip, obscured at left, as they arrive at Baker Street underground station in London for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. (AP Photo/Sang Tan)

Britain's Queen Elizabeth II passes through a ticket barrier at Baker Street underground station in London, for a visit to mark the 150th anniversary of the London Underground, Wednesday, March 20, 2013. The Queen made her first public engagement in more than a week Wednesday after cancellations following her hospitalization for a stomach bug. The British head of state joined her husband Prince Philip and their granddaughter-in-law, Kate, for the event marking the 150th anniversary of London's sprawling subway system, affectionately known as the Tube. (AP Photo/Chris Radburn, Pool)

Male tiger Jae Jae, left, and female tiger Melati, are seen at the new 3.6m pound Sumatran tiger enclosure at London Zoo, north London, as it is official opened by The Duke Of Edinburgh, Wednesday, March 20, 2013. (Photo by Joel Ryan/Invision/AP)

Female tiger Melati is seen in a new 3.6 million pound Sumatran tiger enclosure after it was officially opened by Britain's Prince Philip, the Duke of Edinburgh, at London Zoo, north London, Wednesday, March 20, 2013. (Photo by Joel Ryan/Invision/AP)

Male tiger Jae Jae walks in a new 3.6 million pound Sumatran tiger enclosure after it was officially opened by Britain's Prince Philip, the Duke of Edinburgh, at London Zoo, north London, Wednesday, Mar. 20, 2013. (Photo by Joel Ryan/Invision/AP)

Britain's Prince Phillip, the Duke Of Edinburgh, opens a new 3.6 million pound Sumatran tiger enclosure at London Zoo, north London, Wednesday, March 20, 2013. (Photo by Joel Ryan/Invision/AP)

Britain's Prince Phillip, the Duke Of Edinburgh, opens a new 3.6 million pound Sumatran tiger enclosure at London Zoo, north London, Wednesday, March 20, 2013. (Photo by Joel Ryan/Invision/AP)

Geri Halliwell poses for photographers during the presentation of a new 3.6 million pound Sumatran tiger enclosure officially opened by Britain's Prince Phillip, the Duke Of Edinburgh, at London Zoo, north London, Wednesday, March 20, 2013. (Photo by Joel Ryan/Invision/AP)

Geri Halliwell poses for photographers during the presentation of a new 3.6 million pound Sumatran tiger enclosure officially opened by Britain's Prince Phillip, the Duke Of Edinburgh, at London Zoo, north London, Wednesday, March 20, 2013. (Photo by Joel Ryan/Invision/AP)

Geri Halliwell, center, uses her mobile phone during the opening of a new 3.6 million pound Sumatran tiger enclosure officially opened by Britain's Prince Phillip, the Duke Of Edinburgh, at London Zoo, north London, Wednesday, March 20, 2013. (Photo by Joel Ryan/Invision/AP)