Among those grieving for "Growing Pains" star Alan Thicke, who died of a heart attack yesterday, is his onetime TV son, Leonardo DiCaprio.

The Oscar winner paid tribute to his TV dad in a heartfelt Facebook post that said "no one was cooler" than the actor who played Jason Seaver on "Growing Pains."

"He had tremendous class, a huge heart, and he taught me and so many others the valuable lessons about humility and gratitude," DiCaprio wrote. He added, "I miss him already."

DiCaprio joined "Growing Pains" in its seventh season as homeless teen Luke Brower. This was long before he became the "Titanic" heartthrob and multiple Academy Award nominee.

Last year, Thicke gushed about his TV son, then starring in "The Revenant." "We all recognized there was something special about Leo. He had a great sense of humor, very playful, he could do impressions of all of us and that's something we haven't seen in its full bloom in the movies yet," he told ET Canada. "You had Brad Pitt or Matthew Perry or Hilary Swank, Heather Graham — you know we had some terrific people come through ["Growing Pains"] and the brightest of those was probably Leo."

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