Prince Harry is preparing to turn 40 on September 15 — but it is pretty safe to assume his brother, Prince William, the future King of England, won’t be wishing him a happy birthday.

The renegade royal will enter his fifth decade with an A-list party organized by his wife Meghan Markle, 42, Page Six is told.

But it will be in Montecito, California, 5,000 miles away from the father and brother he grew up with after the tragic death of his mother, Princess Diana, when he was just 12 years old.

This week, Harry was in the same room with William for the first time in over a year — but there was no thawing of the frost that set in after Harry’s infamous Oprah Winfrey interview and the publication of his memoir, “Spare.” It’s said the two brothers, once thick as thieves, did not speak, and William does not want Harry at his own eventual coronation.

Harry, who left the royal family for life in America in 2020, flew back to his homeland to attend a memorial for his uncle, Lord Robert Fellowes, a long-time royal courtier who was married to Princess Diana’s sister, Lady Jane Fellowes.

“William is not speaking to Harry,” said one source. “Harry is not the issue here.”

Another royal insider who has known them both said, “William is furious. I’m not sure what can ever be done to mend fences.”

William, 42, was sent over the edge when Harry wrote in his book about Kate Middleon, blaming her for encouraging him to wear a Nazi costume to a party in 2005. Middleton and King Charles, who have both been battling cancer, were the accused in another book, by reported Markle confidant Omid Scobie, as the “racist” royals who asked what color Harry and Markle’s mixed-race children would be.

On Thursday, both brothers attended the service for Fellowes at St Mary’s Church in Snettisham, close to the royal Sandringham Estate in Norfolk.

However, onlookers said they stood far apart from each other and did not talk.

The Reverend Dan Tansey, who oversaw the service, admitted he was surprised to see both William and Harry at the service which was attended by around 300 people.

He told the Daily Mail, “It was only as I was thanking the congregation as they left that Prince William was shaking my hand, and then very quickly after that, so did Prince Harry.

“It was a surprise but a really pleasant one that they had both come, but maybe less shocking that William was there … I don’t recollect them speaking to each other but there were a lot of family members and friends speaking to them.”

The last time the brothers were in the same place was at King Charles’ coronation last May, and Harry flew back to the US that same day.

As sources told Page Six earlier this summer, Harry would be happy to reunite with his father if he the king allows him and his family — including Markle, son Archie, 5, and daughter Lilibet. 3 — to have royal security in the UK.

“King Charles can give Harry the security clearance he wants so desperately. As the monarch, he is the ultimate decision maker. That would be how father and son can reconcile,” said one royal source.

Harry has repeatedly said he will not bring his wife and children to the UK as long as he does not receive official police security. He and Markle lost their taxpayer-funded police protection detail after they stepped down from being working royals and moved to America.

To this, a palace source told us: “Security provision is decided upon exclusively by a committee called RAVEC in which His Majesty is not involved, though the [royal] household is represented.”

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William (front, with Markle, Harry and wife Kate Middleton) no longer talks to his brother.Getty Images
People magazine reported in July that Harry has attempted to call Charles, but his calls go “unanswered”.

What is clear is that Harry does not plan on opening up yet more fractions with his family. He will not be adding any updates to a paperback version of his bombshell memoir “Spare” when it is released this fall.

As Harry turns 40, sources say he has become “more comfortable” in California and within his life.

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The last time Middleton, William, Harry and Markle — once dubbed the “fab four” — were together was at the funeral of Queen Elizabeth in September 2022.ZUMAPRESS.com
“I think he has his convictions and he is determined, but I also think he’s more unburdened than before,” said a friend.

When the Duke and Duchess of Sussex originally signed a three-book deal with Random House as part of a rumored $20 million contract, announced in 2021, Page Six was told it included Harry’s memoir, a book which Harry and Markle were set to write together and a book from Markle herself.

But we’re now told there are no plans for any more books.

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Both Harry and William this week attended the funeral of their uncle Sir Robert Fellowes (second from left).Getty Images
The Sussexes are currently working with their Archewell Foundation and tied in a recent faux-royal tour of Columbia with plans to promote mental health for young people.

As for the launch of Markle’s lifestyle brand, American Riviera Orchard, sources say that’s still up in the air.

“That is a whole other story,” said one Sussex source.

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Harry talks this aunt, Lady Jane Fellowes, and uncle Earl Spencer, during the unveiling of a statue of Diana, Princess of Wales, in the Sunken Garden at Kensington Palace in July 2021.Getty Images
While her Netflix lifestyle show will debut next year, the couple’s deal with the streamer is also set to end in 2025.

Meanwhile, Harry’s latest chief of staff, Josh Kettle, recently left the job after just three months just before their Columbia trip.

A Sussex pal in California said of the couple, “They are happy and enjoying their lives. You could see that from their trip to Columbia.”

But one longtime friend told the Sunday Times recently that he may have an “enviable lifestyle,” on the surface but, “or the Harry I know, I can’t imagine that gilded exile in California is where he wanted to end up.”