The body was pulled out of the Round Pond by Kensington Palace – where the Duke and Duchess of Cambridge reside with their children when in the capital – last Saturday morning and has yet to be identified.
Metropolitan Police did however reportedly misidentify the body and notified the wrong family that their relative had died.
Artist Endellion Lycett Green, granddaughter of former poet laureate Sir John Betjeman, had been missing for a week ahead of the discovery and the Met had made public appeals in aid of the search for her.
Officers initially thought the body was that of Ms Lycett Green and notified her family, police told the Daily Mail.
Relatives were greatly relieved when Ms Lycett Green, who is known as Delli to friends and family, turned up alive later in the week.
“My sister Endellion is alive, safe and well,” John Lycett Green, her brother, said in a message to friends. “Thank you all for the support and love you showed for Delli and her family.
“Sorry to all of you that, like us, were grieving for the wonder that is Delli. We were told a body was found and was her. It was not, and Delli was found last night.”
Mr Lycett Green added: “RIP the soul that was found in Kensington Round Pond on Saturday morning.”
The body found in the Kensington Palace pond remains unidentified. A spokesperson for Metropolitan Police said: “The death is being treated as unexplained at this time, but is not thought to be suspicious. Inquiries are ongoing.”