With Charlie Sheen's very public meltdown happening during the filming of the latest season of 'Two and a Half Men,' David Letterman was curious if co-star Jon Cryer or anyone else on the show saw any of this coming. On 'Late Show,' Cryer said nobody did.

"This has never happened before," Cryer said. There was no template for a star going what appeared to be crazy while starring in a popular show before.

"It wasn't like, 'Back in 1963 everybody remembers when Fred MacMurray went bats*** and started talking about freemason ninjas and stuff. He was crazy! And Vivian Vance started urinating on the set of 'Here's Lucy.''"

Cryer still considers himself good friends with Sheen, despite everything. "He called you names," Letterman reminded him. "He called you a troll or something."