Kirk Cameron, who played Thicke's son Mike Seaver on 'Growing Pains,' took to his Instagram page to share his memories of working with his on-screen father.
"I spent Monday through Friday for seven important years with Alan Thicke as my 'TV dad,'" he captioned a photo of the two from the show. "I'm shocked and truly heartbroken today at the news of his death. Alan was a generous, kind and loving man. I am so blessed to have grown up with him. Chelsea and I send our love and prayers to his family tonight. We will cherish the memories... 'sharing the laughter and love.'"
Cameron's wife is Chelsea Noble, who played Mike's girlfriend on the long-running series.
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Alan's "TV wife" Joanna Kerns also shared some kind words about Alan on Twitter, in response to actor Daniel Franzese tweeting his condolences to her.
@WhatsupDanny I loved Alan- he was one of the smartest and funniest men I have ever known- we shared a life changing success and friendship
Leonardo DiCaprio, who appeared on the final season of the show, shared a sweet tribute on Facebook as well.
Alan was a devoted father, husband, friend and role model. He knew how to harness the power of the entertainment industry to be a positive influence in so many lives - including mine. I will be forever grateful for the opportunity I had to work with Alan early in my career. He had tremendous class, a huge heart, and he taught me and so many others the valuable lessons about humility and gratitude. I've seen him a number of times over the years and when Alan Thicke walked in the room, quite frankly, no one was cooler. I miss him already - my thoughts and prayers are with the entire Thicke family during this difficult time.
Ashley Johnson, who played youngest daughter Chrissy Seaver on the sitcom, also shared a photo with Alan on social media, but later deleted it.
"There is a sacredness in tears...They are the messengers of overwhelming grief, of deep contrition, and of unspeakable love," she reportedly captioned the photo.
A rep for Jeremy Miller tells TooFab, "Jeremy loves Alan deeply. He has lost a father and is heartbroken."