But according to close friend, former co-star and fellow Scientologist Kirstie Alley — who claims she and the actor fell in love years ago and had an emotional affair — John is not a gay man.
Asked if she thought the rumors could be true, Kirstie "vigorously" shook her head, swooned and told The Sun's Dan Wootton in an interview published on Sept. 16, "No, I don't. I mean, I know him pretty well — and I know the love…"
Kirstie detailed how she and John, who co-starred in 1989's "Look Who's Talking" as well as its two sequels, fell for one another back then but said they did not consummate their feelings because she didn't want to physically cheat on then-husband Parker Stevenson, whom she'd married in 1983.
If she and John had made that choice, she believes it would have been amazing at first but then ultimately would have ended badly. "John and I would have devoured each other because John and I are so alike. It would be like two blazing stars that just fizzled out," Kirstie said.
The whole experience was heartbreaking. "John would agree it was mutual that we sort of fell in love with each other. I will say it's one of the hardest things I've ever done, the hardest decision I've ever made, because I was madly in love with him — we were fun and funny together," she said.
"It wasn't a sexual relationship because I'm not going to cheat on my husband. But you know, I think there are things that are way worse than sexual relationships, than cheating on someone that way," she 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."
Kirstie explained to The Sun that John moved on when he realized nothing would come of their emotional affair. "When it became very apparent that I was staying married, he started seeing Kelly [Preston] again," she said. John married Kelly in 1991.
Kirstie said Kelly once confronted her about her behavior around John in the early '90s. "Kelly came up to me — and they were married then — and she said, 'Erm, why are you flirting with my husband?'" Kirstie recalls. "And that was sort of when I had to make a decision and that was pretty much the end of that."
Kirstie, John and Kelly are now great friends — they all even live next door to one another, Kirstie shared with The Sun, adding that they have a gate in their fence that allows them to visit one another more easily.
Kirstie also said she believes that she and John wouldn't have lasted as a couple long-term if they'd given into their desires all those years ago.
The "Pulp Fiction" actor "goes to bed at like 4 or 5 in the morning and wakes up at 3 in the afternoon. I go to bed at 9 o'clock at night and wake up at 5 in the morning. We basically would have not have seen each other. It would have been a disaster," she added.
"And it turned out great because we've remained best friends all these years."