Prince Philip has been admitted to hospital in London for a planned hip operation, Buckingham Palace said.
At the time of his retirement, Philip had completed 22,219 solo engagements since 1952, gave 5,496 speeches in his travels to more than 76 countries, authored 14 books, served as patron to 785 organizations and made 637 solo overseas visits, Buckingham Palace said.
His Royal Highness, who has been married to Queen Elizabeth II for 70 years, did not attend Easter services with his wife at Windsor Castle on Sunday, April 1.
Britain's Prince Philip, Duke of Edinburgh, in his role as Captain General, Royal Marines, attends a Parade to mark the finale of the 1664 Global Challenge on the Buckingham Palace Forecourt in central London on August 2, 2017.
The health scare comes at a busy time for the royal family. He was absent from the Easter Mattins Service at St George's Chapel where Meghan Markle and Prince Harry will Wednesday in May.
Philip retired from public life a year ago but has since appeared several times at royal engagements alongside the queen.
The Duke, who is the longest-serving consort in British history, has not been in good health in recent times. He will undergo planned surgery on his hip on Tuesday.
Queen Elizabeth paid tribute to her husband in November 1997 during their Golden Wedding Celebrations. This came after the palace originally said that the 96-year-old would "wind down" his workload gradually, though he was keen to carry out his duties.
Philip is now expected to attend Harry and Markle's May 19 wedding at St. George's Chapel with other members of the royal family.