According to The Sun, the woman, Irene Mayor, was knocked down by a police motorbike escorting the Duke and Duchess of Cambridge while they were on their way to Windsor Castle for a Knights of the Garter ceremony.
Witnesses told the publication the bike was on the wrong side of the road and was a police outrider who was clearing traffic for the Royal convoy.
Upon impact, Mayor was thrown into the air and was said to have been taken to the hospital by air ambulance. On Tuesday night, Mayor was reported to be in serious but stable condition with a broken pelvis and other injuries.
A witness told The Sun of the accident, "His bike hit her and she spun round, off her feet and fell badly on the floor."
"The officer was devastated," the person added. "But he was going on the wrong side of the road. It could have been so much worse."
Sources also told the publication Prince William and Kate were "devastated" when informed of the accident. The Duke and Duchess of Cambridge sent flowers to Mayor as an apology and reportedly plan to visit her in person.