Philip, aka the Duke of Edinburgh, was due to make a rare public appearance at the Royal Maundy Service, which took place at St. George's Chapel at Windsor Castle, and then attend a reception and lunch. His 91-year-old wife attended the event without him.
"The duke was keen to attend but made this decision because he has been experiencing some trouble with his hip," the royal source told Reuters.
"The Order of Service was printed some weeks ago when it was hoped the Duke would be able to take part," a Buckingham Palace spokesperson told E! News. "His Royal Highness has since decided not to attend."