In an interview with HuffPost Live, Jon Cryer can still recall when Charlie Sheen's downward spiral all began.

The "Two and a Half Men" revealed to HuffPost Live's Josh Zepps on Thursday that Sheen's decline did not happen overnight, but was a "slowly evolving thing."

Cryer noticed that something wrong was happening with Sheen when he started talking something bizarre about the 9/11 attack.

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That was where it all began and Cryer started notice "all kinds of levels" of misconduct that eventually led to Sheen's dismissal from the show in spring 2011.

Cryer noted that Sheen's "getting married over again, probably a little too quickly," then his subsequent arrest for assaulting his then-wife Brooke Mueller were all manifestations that something wasn't right with him.

"I didn't see the arrest coming, that's for certain," Cryer said.

The actor, who starred in Pretty in Pink, had the idea of Sheen's battle with alcoholism and drug addiction. He even revealed that he was really worried about his Two and a Half Men costar's safety.

"Anyone who's had an addict as a friend knows you live with this fear -- is the next phone call gonna be the one where something horrible has happened?" he recalled.

One thing that Cryer really regretted was that his efforts to help his pal proved fruitless, saying he found it "tough" to deal with that.

"Charlie and I had a couple of conversations. Again, when you're dealing with somebody dealing with a substance abuse problem, it's tough to get through [to them]," he said.

"Clearly I didn't at the time."

But despite Sheen's misconduct, CBS still remained patient at him, believing he would eventually pick himself up. The show eventually got fed up and fired him in 2011.

His role was given to Ashton Kutcher.

Two and a Half Men will end at the 12th season finale later this year.

TagsTwo and A Half Men, charlie Sheen, Jon Cryer