Alley's romantic interest on "Cheers," Ted Danson, was among those who memorialized his late co-star. He shared in a statement to Deadline that he'd actually been watching an old episode of their show on a plane before learning that she'd passed when he landed.
"It was the episode where Tom Berenger proposes to Kirstie, who keeps saying no, even though she desperately wants to say yes," shared Danson. "Kirstie was truly brilliant in it. Her ability to play a woman on the verge of a nervous breakdown was both moving and hysterically funny.
"She made me laugh 30 years ago when she shot that scene, and she made me laugh today just as hard," he continued. "As I got off the plane, I heard that Kirstie had died. I am so sad and so grateful for all the times she made me laugh. I send my love to her children. As they well know, their mother had a heart of gold. I will miss her."
Rhea Perlman, who played the surly Carla on the long-running sitcom, said, "Kirstie was a unique and wonderful person and friend. Her joy of being was boundless."
"We became friends almost instantly when she joined the cast of Cheers," she continued. "She loved kids and my kids loved her too. We had sleepovers at her house, with treasure hunts that she created. She had massive Halloween and Easter parties and invited the entire crew of the show and their families."
"She wanted everyone to feel included," Perlman concluded her statement. "She loved her children deeply. I’ve never met anyone remotely like her. I feel so thankful to have known her. I’m going to miss her very, very much."
Kelsey Grammer, who portrayed Dr. Frasier Crane on "Cheers" and a spinoff based on his character, said, "I always believed grief for a public figure is a private matter, but I will say I loved her." John Ratzenberger took to Twitter, writing, "It's so sad. So very sad. God Bless you and keep you Kirstie Alley."
One of the first to honor Alley on social media was John Travolta, who costarred with Alley in the three "Look Who's Talking" films and was a longtime friend of hers. The two were both Scientologists.
"Kirstie was one of the most special relationships I've ever had," he posted to Instagram shortly after her death was announced. "I love you Kirstie. I know we will see each other again."
Denise Richards, who played Alley's daughter in "Drop Dead Gorgeous," shared a tribute as well -- writing, "Kirstie is one of the funniest, nicest & strongest women I've ever met. I am so lucky & grateful that I got to do a movie with her playing my mom. I was quite intimidated to work with her but she immediately made me feel so comfortable. She had a heart of gold & deep love for animals. Her laugh was infectious & she lit up every room she walked into. Kirstie you are loved by so many & will be so very missed. Prayers to your kids & grandkids."
Her longtime friend Jonathan Knight -- who competed against Alley on the same season of "Dancing with the Stars" -- also shared that his "heart is ripped into a million pieces, and half my soul has been taken away" after her passing.
"We met and connected in a way one rarely gets to experience with others. Through my tears I go through our photos together. I read and reread our texts back and forth. I listen to your voicemails. How did I get to be so lucky to have you in my life?" he wrote. "The time I spent with you is like no other. Your heart was bigger than the Moon. You lived life with so much passion. I’m still processing the fact that you are gone, but find comfort knowing you will always be here in my heart. This picture is one of my favorites with you. I will always remember this exact moment and all the others I shared with you. Thank you for loving me as much I loved you."
William Shatner, who worked with Alley on "Star Trek II," wrote on Twitter, "Saddened to hear of the passing of @kirstiealley. Condolences to her family & friends."
Jamie Lee Curtis, who starred opposite her on "Scream Queens" took to Instagram, writing, "I've just heard the sad news that Kirstie Alley has died. She was a great comic foil in @tvscreamqueens and a beautiful mama bear in her very real life. She helped me buy onesies for my family that year for Christmas. We agreed to disagree about some things but had a mutual respect and connection. Sad news."
Selma Blair commented on Curtis' post, adding, "She was such 💛. She was such a dynamite. Sad news indeed. May her memories be a blessing. Love."
Alley's "Veronica's Closet" co-star Dan Cortese mourned her on Twitter, as well, writing, "Beyond saddened to learn of the passing of the one of a kind @kirstiealley. I was blessed to not only work by her side for 3 seasons, but to call her my friend. Comedy lost a great today. RIP"
On Monday, Alley's children, True and Lillie Parker, announced their mother died after a private battle with cancer. "To all our friends, far and wide around the world ... 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 wrote.
"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," the pair continued. "As iconic as she was on screen, she was an even more amazing mother and grandmother."
Adding they were "grateful to the incredible team of doctors and nurses at the Moffitt Cancer Center for their care," Alley's children said their mother's "zest and passion for life, her children, grandchildren and her many animals, not to mention her eternal joy of creating, were unparalleled and leave us inspired to live life to the fullest just as she did."
"We thank you for your love and prayers and ask that you respect our privacy at this difficult time," the statement concluded.
Alley shared True and Lillie with ex-husband Parker Stevenson, to whom she was married from 1983 until 1997. She was also previously married to Bob Alley from 1970 until 1977.
Alley broke out as Rebecca Howe on "Cheers," for which she won both an Emmy Award and Golden Globe, as well as earning many nominations. She also headlined the shows "Veronica's Closet" and "Fat Actress," had her own reality show, "Kirstie Alley's Big Life," and competed on "Dancing with the Stars,""Celebrity Big Brother" and Season 7 of "The Masked Singer."
On the film side, Alley is known for her work in the "Look Who's Talking" movies, "Star Trek II: The Wrath of Khan," "Summer School," the 1995 "Village of the Damned" remake, "Drop Dead Gorgeous" and "For Richer or Poorer."
She was a spokesperson for Jenny Craig, as well as one of the most famous celebrity Scientologists. In recent years, she became a bit of a controversial figure for her support of Donald Trump.
You can see more celebrity tributes below.
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It’s so sad. So very sad. God Bless you and keep you Kirstie Alley
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She was complex, energetic, animated and hilarious. And she was my friend. Sending my condolences to her family. RIP Kirstie Alley. PS She would’ve agreed with me in saying #fuckcancerpic.twitter.com/CQD5qOr9q5
I just head the news about #KirstieAlley. I’ve not spoke w/ her forever, but have her to thank for launching my career. She told me I was funny every single day on Veronica’s Closet, and I believed her. She threw the best parties and gave the parakeets as our wrap gift. Godspeed.
So sorry we have lost Kirstie Alley. She was a gloriously talented & unique actress and I am delighted I was able to work at her side on occasion. She made me feel welcome. And she made me laugh. As she did so many others. My sympathy to her friends and family. #RIP KirstieAlley
I worked w Kirstie Alley a couple of times many years ago as a guest on CHEERS and she was very welcoming and fun to be around I was just a kid w a small part and she was very lovely She was remarkably funny in everything i saw her do and really fun to watch rehearse RIP
So sad to hear about the passing of @kirstiealley. My very first network TV role was on CHEERS. The whole cast was incredibly kind and welcoming. None more so than she. She was lovely and, of course, hilarious. Condolences to her family. May she Rest In Peace. pic.twitter.com/AHNZWBiNEK