Alley, who's currently competing on Dancing with the Stars, told Walters that Travolta, 58, was the "greatest love of my life."
The actress, 61, admits that she fell hard for the star during the filming of the 1989 movie Look Who's Talkingwhere Travolta played her romantic interest. "Believe me, it took everything that I had, inside, outside, whatever, to not run off and marry John. And be with John for the rest of my life," she told Walters.
When asked why she didn't, Alley replied, "Because I feel like when you marry someone you're supposed to work hard at it, and you're supposed to make it work."
Both actors worked together for the Look Who's Talking sequels, but went on to pursue other romantic relationships. Kelly Preston, a dear friend of Alley's, married Travolta in 1991, while, Alley went on to marry a few times but is currently single.
The actress' full interview with Walters will air on Wednesday on ABC's Good Morning America.
They Dated?! Surprising Celebrity Hookups
Star Sightings: Celebrity Candids
Are These Celebs Too Tan?! Cast Your Vote!