EXCLUSIVE: Truth About John Travolta and Princess Diana's Love Finally Revealed – Including the Shocking Story Behind Their Romantic White House Dance and How Superstar Couple Secretly Stayed in Touch

It's hard to believe it's been 40 years since Princess Diana and John Travolta took a romantic spin at the White House in 1985, but that 15 minutes of magic stunned onlookers, went down in history and sparked an undeniable fire between the dazzling du.

RadarOnline.com can now reveal it was only the tip of the iceberg of their sizzling bond.

"I know for a fact that it was a highlight of being in the United States – it was her favorite moment," recalled Travolta, 71, of the memorable night.

At just 24 years old, Prince Charles' young wife captivated the world.

She had already cemented her place as an international style icon, a devoted mom to two adorable toddler sons and the beloved People's Princess.

But on that night, she was the star of an unforgettable moment in American history.

The occasion was a lavish state dinner, hosted by President Ronald Reagan and First Lady Nancy Reagan.

And the guest list was a dazzling blend of Washington, D.C.'s elite and Hollywood's biggest names – including Clint Eastwood, Tom Selleck, Gloria Vanderbilt – as well as, of course, 31-year-old Travolta, who had skyrocketed to fame with Saturday Night Fever and Grease.

Diana arrived looking every bit the fairytale princess in a midnight blue velvet gown by designer Victor Edelstein, paired with a sapphire and diamond choker.

But what made the night truly legendary was what happened on the dance floor.

Travolta said he hadn't planned to dance with Diana – it was orchestrated behind the scenes.

Then First Lady Reagan discreetly told him the princess wanted to dance with him, but he would need to take the lead.

Travolta revealed: "At midnight, I had to tap her on the shoulder and say, 'Would you care to dance?' She turned around and dipped her head in that Lady Diana way and we were off for 15 minutes dancing."

But seconds before they hit the dance floor, "Shy Di" was suddenly overcome with a panic attack.

"I put my hand in the middle of her back, brought her hand down so that it wouldn't be so high and gave her the confidence that we would do just fine," recalled Travolta, who later described those moments as "like a dream" – admitting he felt like he'd stepped into a movie scene with a breathtaking princess.

The actor added: "I was awestruck with her. She led the way, and I thought: 'Well, that's not going to happen. I've got to go back to my school days of learning ballroom dancing and show that I can lead her.'"

The stunning pair twirled to hits from the soundtracks of Saturday Night Fever and Grease.

Photographers captured the moment, and the images of Diana and Travolta in mid-spin became some of the most famous snapshots of the decade.

But what many don't know is that Diana had originally hoped to dance with someone else, her childhood crush, Mikhail Baryshnikov.

However, that night, the Russian ballet dancer was recovering from an injury and his feet hurt.

Princess Diana later said she'd been just as delighted to dance with the movie hunk.

"I got to be her Prince Charming for the evening," said Travolta. "We bowed when it was over, and she was off, and I was off, and my carriage turned into a pumpkin."

That's when another Hollywood hotshot, Selleck, cut in for a waltz.

While the Magnum, P.I. hunk later confessed he was a bundle of nerves and couldn't come up with any small talk, he said he did better than Princess Diana's next dance partner – movie tough guy Eastwood.

"He went next and was really out of his safety zone," said Selleck, now 80.

Turns out then-55-year-old Eastwood blurted out: "You're too old for me" to Princess Diana, who replied: "But I'm only 24."

After their dance, Travolta admitted he couldn't shake off Princess Diana's aura.

"She was charming, adorable and down to earth," he said. "That was one of the highlights of my life."

A palace insider said: "She was in awe of him. From a young age, Diana always wanted to be a dancer, and the pair desperately wanted to stay in touch after their dance – and secretly did by letter."

In his diary, a delighted President Reagan wrote: "Everyone danced like at a Junior Prom."

At the time, Prince Harry was only 1 year old, Prince William was 3, with the dance with Travolta making Princess Diana feel like a young girl again, sources said.

But the sexy spectacle didn't sit well with her stodgy hubby, Charles.

Soon after, he held a press conference with American reporters, who were instructed to only ask questions about a British art exhibit – but all they wanted was dish on Princess Diana's big night.

"The princess will not be answering questions," said Charles as Diana sat silently beside him.

But he quickly admitted: "She did enjoy dancing with John Travolta," as Di dropped her eyes and smiled under her broad-brimmed hat.

Although Diana had always dreamed of becoming a ballerina, her 5-foot-10 height made it impossible.

She decided to limit her dreams of performing to corresponding with other dance lovers, especially handsome Travolta in America.

The pretty royal was known for her volume of correspondence and secret love letters.

"Oh yes, Diana was quite enamored with Mr. Travolta," a palace insider said later. "She was a starry-eyed type of woman. I'm sure she dreamed about him and wrote to him."

But the actor – who married actress Kelly Preston six years later – has gallantly stayed silent on Diana's secret letters to him, we can reveal.

Even decades later, Travolta will only say: "So I feel I made her life better she made my life better... I'm very sorry that she's not here."

After Diana's death in a Paris car crash in 1997, the A-lister expressed his deepest sorrow, saying: "I was devastated when she passed. There are moments in your life you never forget, and that was one of them."