William has been given the go-ahead to throw the bash at his grandmother's Windsor Castle home or at Sandringham Estate later this summer.
His wife Kate will also be included in the celebrations after her own 40th party plans in January were cancelled due to rising Covid cases.
WATCH: Prince William turns 40: how he's shaping the future of the royal family
No further details have been reported, but it's understood the Queen, 96, will decide whether to attend on the day of the party due to her ongoing mobility issues.
The royals usually mark milestone birthdays in a special way. One such lavish bash was the Dance of the Decades party at Windsor Castle in June 2000 to celebrate Prince Andrew's 40th birthday, Princess Anne's 50th, Princess Margaret's 70th and Prince William's 18th.
The couple are reportedly hosting a joint 40th birthday party this summer
William turned 40 on Tuesday, with Kensington Palace releasing three photos of the future King to mark the occasion. He was pictured selling copies of The Big Issue on the streets of London to highlight homelessness, an issue he was first introduced to by his mother Princess Diana and something he has been particularly passionate about since his younger years.
Writing in The Big Issue, William shared: "I have always believed in using my platform to help tell those stories and to bring attention and action to those who are struggling.
William helped sell copies of The Big Issue © Andy Parsons/The Big Issue
"I plan to do that now I'm turning 40, even more than I have in the past. So, for my part, I commit to continue doing what I can to shine a spotlight on this solvable issue not just today, but in the months and years to come.
"And in the years ahead, I hope to bring George, Charlotte and Louis to see the fantastic organisations doing inspiring work to support those most in need – just as my mother did for me."
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