The actress, who died at age 71 on Monday after a recent cancer diagnosis, starred alongside Travolta in 1989's Look Who's Talking, plus two sequels: Look Who's Talking Too (1990) and Look Who's Talking Now (1993).
And back in 2018, during her time on Celebrity Big Brother U.K., she revealed that she thought she "kissed Travolta" — and furthermore, "almost ran off and married" him.
"I did love him; I still love him," she said at the time. "If I hadn't been married, I would've gone and married him and I would've been in an airplane because he has his own plane."
Her passion for the actor developed after starring together in the Look Who's Talking films in which Alley and Travolta, 68, play love interests James and Mollie Ubriacco (née Jensen), who meet by chance when Mollie jumps into a taxi after going into labor.
Mollie plans on raising her son as a single mother, as she recently learned the man she conceived the baby with does not plan to stay with her.
SNAP/REX/Shutterstock Kirstie Alley and John Travolta in Look Who's Talking (1989)
But she and the taxi driver, Travolta's James, end up falling in love and raising their family (which eventually also includes daughter Julie) together. The films chronicle the pair's ups and downs, and the first even includes a scene where James — who also happens to be a pilot, just like Travolta — takes Mollie up in his plane.
And in real life, Alley told Howard Stern in 2013 that she never felt about anyone the way she felt about Travolta, explaining the feelings were mutual.
Jim Smeal/Ron Galella collection/getty Kirstie Alley and John Travolta in 1989
But despite Travolta allegedly feeling the same way, they didn't act on their feelings, as Alley was married to Parker Stevenson at the time. (The two divorced in 1997, while Travolta married Kelly Preston, who died of breast cancer in 2020, in 1991.)
"It took me years to not look at John as a romantic interest," she said, adding that he was "the greatest love of my life."
In September 2018, Alley went into more detail about how she fell in love with her costar in the late '80s, saying on the Dan Wootton Interview podcast that not sleeping with Travolta was "one of the hardest things I've ever done."
"[It was] the hardest decision I've ever made because I was madly in love with him — we were fun and funny together," said the Cheers alum. "It wasn't a sexual relationship because I'm not going to cheat on my husband."
Bei/Shutterstock John Travolta and Kirstie Alley
"But, you know, I think there are things that are way worse than sexual relationships, than cheating on someone that way," Alley added. "I consider what I did even worse because I actually let myself fall in love with him and stay in love with him for a long time."
Alley went on to admit that she continued flirting with the Grease superstar even after he married Preston in 1991 — that is, until Preston herself put an end to it.
"Kelly came up to me, and they were married then, and she said, 'Erm, why are you flirting with my husband?' " Alley said. "And that was sort of when I had to make a decision and that was pretty much the end of that."
"John and I would have devoured each other because John and I are so alike," the Veronica's Closet actress said. "It would be like two blazing stars that just fizzled out."
Matt Winkelmeyer/Getty Kirstie Alley and John Travolta
RELATED GALLERY: Remembering Kirstie Alley's Life in Photos
Alley died after a short battle with cancer, her children announced on her Instagram page Monday night.
In the statement announcing her death, True and Lillie began, "We are sad to inform you that our incredible, fierce and loving mother has passed away after a battle with cancer, only recently discovered."
They continued in part, "She was surrounded by her closest family and fought with great strength, leaving us with a certainty of her never-ending joy of living and whatever adventures lie ahead. As iconic as she was on screen, she was an even more amazing mother and grandmother."
Reacting to the loss, Travolta shared a stunning throwback photo of Alley and added another of them smiling at one another.
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"Kirstie was one of the most special relationships I've ever had," he said of the late actress. "I love you Kirstie. I know we will see each other again."
Travolta also shared a clip and himself and the late actress performing "The Dance of Love" in Look Who's Talking Now on his Instagram Story.