Kevin Costner has spilled a royally good secret.

The Oscar winner said Princess Diana was interested in starring in a sequel to his film “The Bodyguard,” playing a woman his character was hired to protect but winds up falling for, similar to the role played by Whitney Houston in the original movie.

“The studio liked the idea of doing a ‘Bodyguard 2’ (with Princess Diana) in the same kind of capacity as Whitney,” Costner told People TV. “Nobody really knew that for about a year.”

Costner, who currently stars on Paramount Network’s “Yellowstone,” said he told the princess the role was made specifically for her.

“I said, ‘Look, I’m gonna write this part with you in mind. Is this something that you would like to do?’” he recalled. “And she said, ‘Yes, I do.’

“I just remember her being incredibly sweet on the phone, and she asked the question. She goes, ‘Are we going to have, like, a kissing scene?’

“She said it in a very respectful — she was a little nervous because her life was very governed. And I said, ‘Yeah, there’s going to be a little bit of that, but we can make that OK, too,’” he said.

Costner, 64, managed to get Diana on the phone thanks to the efforts of someone else in the royal family, Sarah Ferguson, the Duchess of York.

“Sarah was really important,” Costner said. “I always respect Sarah because she’s the one that set up the conversation between me and Diana. She was the one that set it up, and she never said, ‘Well, what about me? I’m a princess too.’ She was just so supportive of the idea.”

“The Bodyguard” came out in 1992. Princess Diana died in 1997.

Costner’s intel about the proposed film follows his revelation that Houston was not the actress in his arms on the poster for “The Bodyguard.” He admitted the singer had already left the set so they used her double.