Hell hath no fury like two royals on the outs.

Prince William was so angry at younger brother Harry that he refused to break bread with him at the infamous Sandringham Summit, where the whole family tried to sort out the Megxit mess.

The revelation is just one in a new bombshell book, serialized in the Daily Mail.  The release date is set for Oct. 13.

In “Battle of Brothers,” author Robert Lacey claims the royal’s once-warm relationship has been “utterly broken” by Harry’s “disrespect” and betrayal when he didn’t consult the Queen before he and wife Meghan Markle told the world that they were ditching their royal duties.

The Duke and Duchess of Sussex, in fact, told the palace of their decision only 10 minutes before they tweeted the big news.

When the brothers came face-to-face at the summit, the 38-year-old William did all he could to avoid Harry, 36, outside the official negotiations, William’s friends told Lacey.

“The Queen had suggested the family should gather for lunch before their big pow-wow in the library that afternoon, but he refused his grandmother’s invitation,” Lacey write about William. “He would obviously turn up at 2 p.m. for the meeting, he said, but he only wanted to talk business.”

The two princes have barely said a word to each other since then, except to wish each other a happy birthday.

Adding injury to insult was the decision by the Duke and Duchess of Sussex to trademark Sussex Royal products without his grandmother’s OK. The family saw the move as  “commercializing of the crown,” Lacey claims.

Royal heads hit the roof: “‘Hopping’ was a mild description of how mad the family was.”