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Britain's Catherine, Duchess of Cambridge talks to runners as she prepares to take part in a relay race, during a training event to promote the charity Heads Together, at the Queen Elizabeth Olympic Park in London, on February 5, 2017. The Duke and Duchess of Cambridge and Prince Harry join a training day with the runners taking part in the 2017 Virgin Money London Marathon for Heads Together, the official Charity of the Year. / AFP PHOTO / POOL / Alastair Grant (Photo credit should read ALASTAIR GRANT/AFP/Getty Images)

Britain's Catherine, Duchess of Cambridge talks to runners as she prepares to take part in a relay race, during a training event to promote the charity Heads Together, at the Queen Elizabeth Olympic Park in London, on February 5, 2017. The Duke and Duchess of Cambridge and Prince Harry join a training day with the runners taking part in the 2017 Virgin Money London Marathon for Heads Together, the official Charity of the Year. / AFP PHOTO / POOL / Alastair Grant (Photo credit should read ALASTAIR GRANT/AFP/Getty Images)
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LONDON, UNITED KINGDOM - FEBRUARY 05: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 48 HOURS AFTER CREATE DATE AND TIME) Catherine, Duchess of Cambridge takes part in a running race against Prince William, Duke of Cambridge and Prince Harry as they join a Team Heads Together London Marathon Training Day at the Queen Elizabeth Olympic Park on February 5, 2017 in London, England. (Photo by Max Mumby/Indigo/Getty Images)

LONDON, UNITED KINGDOM - FEBRUARY 05: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 48 HOURS AFTER CREATE DATE AND TIME) Catherine, Duchess of Cambridge takes part in a running race against Prince William, Duke of Cambridge and Prince Harry as they join a Team Heads Together London Marathon Training Day at the Queen Elizabeth Olympic Park on February 5, 2017 in London, England. (Photo by Max Mumby/Indigo/Getty Images)
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Britain's Catherine, Duchess of Cambridge (L), Britain's Prince William, Duke of Cambridge (C) and Britain's Prince Harry (R) take part in a relay race, during a training event to promote the charity Heads Together, at the Queen Elizabeth Olympic Park in London, on February 5, 2017. The Duke and Duchess of Cambridge and Prince Harry join a training day with the runners taking part in the 2017 Virgin Money London Marathon for Heads Together, the official Charity of the Year. / AFP PHOTO / POOL / Alastair Grant (Photo credit should read ALASTAIR GRANT/AFP/Getty Images)

Britain's Catherine, Duchess of Cambridge (L), Britain's Prince William, Duke of Cambridge (C) and Britain's Prince Harry (R) take part in a relay race, during a training event to promote the charity Heads Together, at the Queen Elizabeth Olympic Park in London, on February 5, 2017. The Duke and Duchess of Cambridge and Prince Harry join a training day with the runners taking part in the 2017 Virgin Money London Marathon for Heads Together, the official Charity of the Year. / AFP PHOTO / POOL / Alastair Grant (Photo credit should read ALASTAIR GRANT/AFP/Getty Images)
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LONDON, UNITED KINGDOM - FEBRUARY 05: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 48 HOURS AFTER CREATE DATE AND TIME) Catherine, Duchess of Cambridge talks with Paula Radcliffe as she joins a Team Heads Together London Marathon Training Day at the Queen Elizabeth Olympic Park on February 5, 2017 in London, England. (Photo by Max Mumby/Indigo/Getty Images)

LONDON, UNITED KINGDOM - FEBRUARY 05: (EMBARGOED FOR PUBLICATION IN UK NEWSPAPERS UNTIL 48 HOURS AFTER CREATE DATE AND TIME) Catherine, Duchess of Cambridge talks with Paula Radcliffe as she joins a Team Heads Together London Marathon Training Day at the Queen Elizabeth Olympic Park on February 5, 2017 in London, England. (Photo by Max Mumby/Indigo/Getty Images)
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Britain's Prince Harry (L), Britain's Catherine, Duchess of Cambridge (R) and Britain's Prince William, Duke of Cambridge (C) react after taking part in a short relay race, during a training event to promote the charity Heads Together, at the Queen Elizabeth Olympic Park in London, on February 5, 2017. The Duke and Duchess of Cambridge and Prince Harry join a training day with the runners taking part in the 2017 Virgin Money London Marathon for Heads Together, the official Charity of the Year. / AFP PHOTO / POOL / Alastair Grant (Photo credit should read ALASTAIR GRANT/AFP/Getty Images)

Britain's Prince Harry (L), Britain's Catherine, Duchess of Cambridge (R) and Britain's Prince William, Duke of Cambridge (C) react after taking part in a short relay race, during a training event to promote the charity Heads Together, at the Queen Elizabeth Olympic Park in London, on February 5, 2017. The Duke and Duchess of Cambridge and Prince Harry join a training day with the runners taking part in the 2017 Virgin Money London Marathon for Heads Together, the official Charity of the Year. / AFP PHOTO / POOL / Alastair Grant (Photo credit should read ALASTAIR GRANT/AFP/Getty Images)
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