An elderly woman is in a "serious but stable condition" in hospital after she was struck by a police motorbike escort for Prince William and Kate, according to UK media reports.
The Duke and Duchess of Cambridge were travelling from London to Windsor on Monday afternoon when the accident occurred, the BBC reported.
An 83-year-old woman, identified as Irene Mayor, was injured in a collision in southwest London and taken to hospital in a critical condition.
Her condition has now stabilised, according to the BBC.
A Kensington Palace spokesperson told the British broadcaster the Royal couple was "deeply concerned and saddened" and had been in touch with the woman.
"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," the palace spokesperson said.
The Sun reported that a police escort was clearing traffic for Prince William and Kate's convoy when the accident happened.
The woman's daughter, Fiona, told the newspaper that her mother had "lots of injuries" though did not specify what they were.
Britain's police watchdog, the Independent Office for Police Conduct (IOPC), is investigating the incident.
"The investigation is in its very early stages and the officer involved is assisting our enquiries as a witness," an IOPC spokesman told the BBC.
"Our immediate thoughts are with the injured woman and her family and those affected by the incident."
The Royal couple have reportedly sent flowers to the elderly widow.
The incident comes just months after a woman was injured in a car crash involving Prince Philip near the Royal family's Sandringham Estate.
The 97-year-old Duke of Edinburgh voluntarily surrendered his driver's licence soon after.