Royal commentator Tom Bower described Prince Harry’s memoir Spare “make or break”.
Speaking to The Sun, he added: “I imagine that King Charles has been warned that any retaliation won’t be pretty.
“All that King Charles can really do is to withhold the titles for his grandchildren Archie and Lilibet.
“Ultimately, I suppose, he could take away Harry and Meghan’s titles as well, but that’s pretty drastic.
“I don’t know what else he can do. If it is as bad as I think it is, then Harry and Meghan have gone fully rogue.
“The best the family can do is to break ties with them.”