A woman in her 80s is in a serious condition in hospital after an accident involving the Duke and Duchess of Cambridge's convoy.
William and Kate were on their way to a ceremony in Windsor on Monday when a marked police motorbike in their convoy was involved in a collision with the woman on Upper Richmond Road, Richmond, south-west London.
The woman was taken to hospital in a critical condition, Scotland Yard said.
The duke and duchess are "deeply concerned and saddened" by what happened and have been in touch with the woman who they say is called Irene, Kensington Palace said.
The Independent Office for Police Conduct (IOPC) is investigating the circumstances of the collision which involved a motorcycle attached to the Royalty and Specialist Protection Command.
An IOPC spokesman said: "The woman, in her 80s, suffered serious injuries and was taken to a London hospital where she remains in a serious but stable condition.
"In line with procedure, the Metropolitan Police Service referred the collision to the IOPC.
"Our staff attended the scene of the incident and after careful consideration, we have launched an independent investigation.
"The investigation is in its very early stages and the officer involved is assisting our enquiries as a witness.
"Our immediate thoughts are with the injured woman and her family and those affected by the incident."
Kensington Palace said: "The Duke and Duchess of Cambridge were deeply concerned and saddened to hear about the accident on Monday afternoon.
"Their Royal Highnesses have sent their very best wishes to Irene and her family and will stay in touch throughout every stage of her recovery."
It is understood that the couple have sent flowers.
The accident took place at around 12.50pm on Monday when the royal couple were on their way to Windsor for the St George's Chapel service commemorating the Order of the Garter.
Earlier this year, the Duke of Edinburgh, 98, surrendered his driving licence after a crash at Sandringham.
Philip flipped his Land Rover Freelander on January 17 after colliding with a Kia as he pulled out onto the A149 in Norfolk.