Sheen and his sibling Emilio Estevez grew up with Penn and his brother Sean, and his father Martin Sheen was one of the first to arrive on the scene of the mystery death to comfort the Reservoir Dogs star's mother.
The 25-year-old, who co-starred with Penn in new movie The Darwin Awards, was devastated when he heard the 43-year-old actor's body had been discovered at his California condominium on Tuesday.
Speaking from a screening of The Darwin Awards at the Sundance Film Festival last night, Valderrama paid tribute to his pal.
He said, "He was an incredibly talented actor and just a very wonderful person. It's so sad. We all feel it's a very big loss."
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