Princess Kate blocked sister-in-law Meghan Markle from attending King Charles’ upcoming coronation, a prominent royal biographer claims.

Tom Bower, who penned the best-selling “Revenge: Meghan, Harry, and the War Between the Windsors,” made the shock declaration during an interview with GB News on Thursday, saying he believed Markle may actually have wanted to attend the historic event.

“We must all be grateful that Kate, in the end I think, prevented Meghan from coming, and said she ‘wouldn’t have her there under any circumstances’,” the author claimed. “And if she [Markle] did come, she’d have to sit at the back.”

“I do think that for the Royal Family, Harry’s presence is constitutionally important,” Bower continued. “God forbid, the Cambridges all died, we’d have King Harry on the throne after Charles, so he’s got to be there.”

Buckingham Palace confirmed on Tuesday that Prince Harry will head to London to attend the coronation alone on May 6. Markle, meanwhile, will stay in California with the couple’s two children, Prince Archie and Princess Lilibet.

Bower’s belief that it was Kate who was behind the bombshell decision to have Markle iced out of the event comes after details about the pair’s frosty relations were revealed in Harry’s memoir, “Spare.”