Just one day after Charlie Sheen revealed he is HIV-positive, the actor's father, Martin Sheen, admitted he is immensely proud of his son for opening up about his diagnosis.

"He had been leading up to this sort of story for several months, and we kept encouraging him to do it. And he kept backing away and backing away because it was like going to his own execution, I guess. It was the most difficult thing he'd ever done," Martin, 75, said of Charlie's tell-all interview on Today.

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Charlie during his Today interview on Tuesday, Nov. 17.

"We didn't know until he walked on the set this morning that he was going to do it. I saw him Saturday night, my wife and I went to see him to make sure he knew we were behind him, and if he wanted me to go, I would have… He said, no, this was his and his alone," the actor told the Naples Daily News of his 50-year-old son on Tuesday, Nov. 17.

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Charlie and Martin in February 1991.

According to the Florida news outlet, Martin then became visibly "choked up" while talking about Charlie's brave decision to reveal he had been diagnosed with HIV nearly four years ago. "This morning, as I watched him alone, reveal his deepest, darkest secret, I couldn't believe the level of courage I was witnessing and that it was my son. I left him a message, and I said that if I had that much courage, I would change the world," he added.