The Oscar winner took to Facebook on Wednesday to pay tribute to his former Growing Pains co-star, who died after suffering a heart attack while playing hockey with his 19-year-old son, Carter, on Tuesday.
"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," DiCaprio shared.
The 42-year-old actor's Growing Pains character, Luke Brower, was a homeless teen taken in by the Seaver family on the final season of the sitcom from 1991 to 1992, when DiCaprio was just 18 years old.
"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," DiCaprio continued. "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," he concluded.
DiCaprio was far from the only celebrity to pay tribute to the TV icon. Thicke's famous friends and former co-stars took to social media to remember the actor, including his son, Robin.
"My Father passed away today. He was the best man I ever knew. The best friend I ever had. Let's all rejoice and celebrate the joy he brought to every room he was in. We love you Alan Thicke," the 39-year-old singer wrote on Instagram late Tuesday night. "Thank you for your love. Love, you grateful son."