09/14/2006 AT 08:25 AM EDT
Speaking publicly for the first time since his younger brother Chris's death
earlier this year, Sean Penn says, "The problem was weight."
"He had certainly been a fantastically self-abusing guy over periods of his life, but that wasn't the case in the end," Penn, 46, tells CNN's Larry King in an interview airing Thursday. "I mean, it was a natural death. But a natural death that was brought on by some hard living, but particularly weight."
Chris Penn, who reportedly weighed 300 lbs. at the time of his death, was found dead in his Santa Monica condo on Jan. 24. According to the coroner, the 40-year-old actor's official cause of death was an enlarged heart, though Valium, morphine and marijuana as well as an antihistamine and a high level of codeine were also found in his system.
Penn, who stars in the upcoming movie All the King's Men,
tells King he and his brother were "very close. The thing that summed it up the best for me was a friend of mine who I saw a couple of days after it happened, saw me and walked across a lobby in a hotel, and he said, 'It's a stinker.' "
Of losing a sibling, he says, "It's a piece of you. I'm one of three, so I'm either my right, left arm or the center at various times, and each was the other, so I intermittently have lost my right arm, the left or in the center, but that's life and people go through that."
He also praises his late brother's acting skills. "I think he was a size of soul that nobody else had, and this isn't a brother talking. All you need to do is watch the ironically titled The Funeral
that my brother Christopher was in. It's a piece of work that always inspired in me. I mean, he was a size of talent and a size of person that I don't think anybody else had."