The King has been seen smiling as he made his first public appearance since his stay in hospital.
The monarch, joined by the Queen and a member of the clergy, attended a Sunday service at St Mary Magdalene Church in Sandringham, Norfolk.
He waved to onlookers during his first time out in public since being discharged from the London Clinic last Monday.
The King underwent a procedure for an enlarged prostate, spending three nights in hospital.
While the Queen told patients he is “doing well” during a visit, Sky News understands he could take up to a month off from public duties as he recuperates.
The Princess of Wales has also been recovering from abdominal surgery after spending two weeks in hospital, and Prince William has taken a break from royal events to support his family.
It means Camilla is now the most senior member of the Royal Family carrying out public engagements while both the King and the princess recover.
The King is understood to have wanted to share the news of his prostate treatment to encourage other men to get themselves checked.
It comes after Sarah Ferguson, Duchess of York, shared she was diagnosed with skin cancer in January.