JOHN TRAVOLTA and PRINCESS DIANA steamed up the White House with their famously flirty dance – but when the party ended, the “Saturday Night Fever” hunk went to bed with a MAN!

That’s the shocking secret Travolta has hidden from the world for 28 years, his ex-gay lover, Doug Gotterba, told TheENQUIRER.

In an iconic photo, the tuxedo-clad star twirled the stunning royal beauty across the White House dance floor in November 1985.

But when the Hollywood heartthrob returned to his five-star hotel suite that historic night, his male lover Doug was waiting for him!

“John looked very handsome in his tux and he was convinced that Diana was physically attracted to him,” Doug, who claims to have been involved with Travolta for six years, told The ENQUIRER.

“If Diana only knew the truth!”

Travolta has gushed about his big night with the late princess, but he never mentioned that Doug, his personal pilot-turned-bedmate, was his REAL date that night.

“Suddenly, I was the only thing in America that mattered to Princess Diana, and I was reborn,” the “Grease” star told one reporter, adding that he felt “like a frog who’d been turned into a prince.”

According to Doug, Travolta was elated on that magical night when then-President Ronald Reagan and wife Nancy, hosted a gala state dinner to honor Diana, then 24, and her husband Prince Charles.

“When John got back to the hotel, he was over the moon!” Doug recalled. “He said First Lady Nancy Reagan whispered in his ear that Diana wanted to dance with him and he should ask her.”

With other A-listers, including Clint Eastwood, Tom Selleck and Neil Diamond, looking on, the couple danced to two tunes from his movie “Saturday Night Fever,” played by the U.S. Marine Band.

Doug added: “John cherished the moment like it was his own.”