The Duke and Duchess of Cambridge will hold a joint 40th birthday party later this summer

The pair plan to follow tradition to "celebrate their landmark birthdays in style" by collaborating on their celebrations and have been given the go ahead to invite people to either Windsor Castle or the Sandringham Estate for their bash.

However, according to the Daily Mirror newspaper, Queen Elizabeth won't confirm if she'll be joining her family at the party until the day of the bash because of her ongoing mobility issues.

When Catherine turned 40 earlier this year, she had an intimate celebration with friends and family at her Anmer Hall home in Norfolk amid concerns about the Omicron variant of coronavirus.

At the time, a source said: "There are likely to be low-key celebrations for the Duchess. She didn't want anything flashy anyway - that's not exactly her thing - but particularly given the current climate anything is likely to be scaled down."

A similar big party was staged in Windsor in June 2000, when William turned 18, Prince Andrew turned 40, Princess Anne turned 50, and the late Princess Margaret turned 70.

Meanwhile, for the first time, William's birthday will not be marked by the flying of the Union flags over government buildings.

Instead, only the queen and Prince Charles will have the honour this year.

It is believed the decision was made in a bid to save Prince Andrew from embarrassment after a number of councils across the country had said they wouldn't obey the protocol to fly the flag on his birthday because of his now-settled lawsuit with Virginia Roberts, who had accused him of sexually abusing her when she was 17, a claim he has denied.