Prince William is reportedly seething over Prince Harry’s stunning return to Britain — amid fears the estranged brothers could soon be pushed into a deeply uncomfortable royal reunion.

The future king, 44, is said to be “apoplectic” over the prospect of Harry and Meghan Markle spending significantly more time in the U.K., potentially blowing open one of the Royal Family’s ugliest feuds.

Harry, 41, has spent years at war with his brother after quitting royal life with Meghan in 2020 and moving to California.

What followed was a barrage of damaging accusations involving William, Kate Middleton, King Charles and Queen Camilla — leaving the once-inseparable brothers barely speaking.

Now Harry’s return could force William into the very confrontation he has reportedly spent years avoiding.

Former royal correspondent Peter Hunt warned that Harry being back on British soil would make it much harder for William to simply keep his distance.

“His presence back home will make it harder for his brother to duck a reconciliation,” Hunt said.

And he believes William will be furious.

“The surprise return of Harry and Meghan is likely to have left William apoplectic.”

Even more dramatically, Hunt suggested the Sussexes’ comeback could create two competing royal power centers — one surrounding William and another surrounding Harry.

“In the long term, the return of the Sussexes to the U.K. opens up the prospect of two rival courts,” he said.

The timing of Harry and Meghan’s reported return is also raising serious questions.

Royal expert Richard Fitzwilliams believes the couple may be making their move now because King Charles is still on the throne.

Once William becomes king, Fitzwilliams warned, the door may slam shut.

“This is actually an extremely serious situation,” he said.

Fitzwilliams suggested William could take a much harder line on Harry and Meghan once he controls the monarchy — possibly even examining their royal titles and those of their children.

“I strongly suspect that William would look very closely at their titles and possibly the titles of their children,” he said.

He added that William could see the Sussexes’ return as proof they “couldn’t be trusted for a single second.”

The move is also being viewed by some royal watchers as a humiliating reversal for Harry and Meghan after six years of trying to build a new life in America.

Their Hollywood ambitions have repeatedly been questioned, and a return to Britain would mark a dramatic change from the couple who once seemed determined to stay far away from royal life.

And this may not be a quick visit.

Ailsa Anderson, Queen Elizabeth II’s former press secretary, believes Harry and Meghan could be back for the long haul — especially if their children are enrolled in British schools.

“You can’t flip-flop every two minutes and take them out of school and go back to the United States and then come back to the U.K.,” she said.

That could leave William facing an uncomfortable new reality: Harry may once again be a permanent presence on his doorstep.

Harry’s apparent change of heart is especially striking because he has repeatedly complained about security concerns in Britain.

But Anderson believes a recent emotional visit to Althorp, Princess Diana’s ancestral home, may have changed something inside him.

After six years away, Harry may finally be feeling the pull of home.

For William, however, his brother’s return could mean the royal feud he hoped to keep at arm’s length is about to explode back into public view.