Queen Elizabeth II's husband Prince Philip will on Monday celebrate his 92nd birthday in the London hospital where is recovering from exploratory abdominal surgery, AFP reports.
The colourful royal was said by Buckingham Palace to be "progressing satisfactorily" after undergoing the operation at the London Clinic on Friday.
The palace would not reveal if the queen, 87, and other members of the family were to visit the duke, who is expected to spend up to two weeks in hospital while his results are analysed.
The occasion will be marked by traditional gun salutes at the Tower of London and Hyde Park, according to officials.
The queen spent the weekend at her Windsor Castle residence, but carried out an engagement at the BBC's refurbished headquarters in London on Friday.
She told presenter John Humphrys "I don't know" when asked about her husband's recovery, but added "he's not ill".
Philip was taken to hospital by car for the planned appointment shortly after attending a Buckingham Palace garden party on Thursday evening.
The duke was born Prince Philippos of Greece and Denmark on June 10, 1921, the only son of prince Andrew of Greece, the younger brother of Greece's king Constantine.
He attended preparatory school in England and served in the Royal Navy during World War II before his military career was cut short by the death of his wife's father king George VI in 1952, which put her on the throne.
The couple have been married since 1947, making Philip the longest-serving royal consort in British history.
The queen once described him as "my strength and stay all these years".
The duke's "trial and error" approach to public life and earthy humour have occasionally landed him in hot water, but such gaffes provided good copy for royal reporters covering the round of official openings and engagements.
"You managed not to get eaten, then?" was one typical remark to a British student who had trekked in Papua New Guinea in 1998.
On a visit to China in 1986, he warned a group of British students: "If you stay here much longer, you'll all be slitty-eyed."
Philip has now been hospitalised four times in two years, but aides insist he is generally in good health.
He was admitted to hospital twice last summer for a bladder infection, missing the last event of the queen's diamond jubilee celebrations in June as a result.
He also spent Christmas 2011 in hospital after being rushed to hospital with a blocked coronary artery, which required surgery.
Despite his health problems, the duke has maintained a hectic schedule and conducted a visit to Canada in April.