The queen, who had mobility problems, did not attend the service in the chapel of St. George in the area of the castle, an item in the royal diary.
William and Catherine accompanied two of their three children: Prince George, 8, and 6-year-old Princess Charlotte.
Also present were the Queen’s youngest son, Prince Edward, with his wife Sophie and their children, and Princess Eugenia, daughter of Prince Andrew.
The queen, who turns 96 on Thursday, celebrates her Platinum Jubilee this year, completing 70 years on the throne.
She has been out of public office by order of her doctors since spending one night in hospital in October and also had a COVID-19 crisis in February. She attended a memorial service last month for her late husband Prince Philip and has continued to meet with diplomats and politicians.
On Thursday he had a visit from Prince Harry’s grandson and the Duchess of Sussex – the first time the couple have visited the UK together since resigning as royal family in 2020 and moving to California.
Harry and Megan visited the Queen in Windsor, 32 miles west of London, on their way to the Netherlands for the Invictus Games. Harry is the founder and patron of the International Wounded and Sick Military Competition for Soldiers and Veterans.
