Philip, the Duke of Edinburgh, married Elizabeth in 1947 and has been by his wife’s side throughout her reign, the longest in British history.
“The duke is in perfectly good health, he is just spending the day privately,” the royal source said.
Former naval officer Philip, who had successful hip replacement surgery earlier this year, retired from public life last year, quipping at the time that he was no longer able to “stand up much”.
Senior members of the royal family traditionally attend a Christmas service at the St Mary Magdalene church in Sandringham, eastern England.
Elizabeth attended, as did Charles, Prince of Wales, heir to the throne. Charles’ wife, Camilla, did not attend, according to a Reuters photographer at the church.
Charles’ sons, Princes William and Harry, also went to the service with their wives, Kate and Meghan.