Blair played his love interest on the show, but reportedly was fired after complaining about Sheen's alleged frequent lateness and poor work ethic.
Sheen had not spoken publicly about Blair's ouster since he announced it in June, but he clarified the circumstances surrounding her departure this week.
"One of our primary characters, Selma Blair, who played Kate, was written out because [the show] was not about our relationship, and the problem was too many people were still excited about the 'Two and a Half [Men]' character and thought the 'Anger Management' character was a little dull," Sheen said on Wednesday's edition of "The Tonight Show."
"So, um, that is not the case anymore," he said. "Her character leaves, and I start circling the drain. So, it's really fun to watch and hella fun to play."
"Anger Management" airs Thursday nights on FX.
Sheen was famously fired in 2011 from his hit series "Two and a Half Men" after eight seasons because of his drug use, insubordination and erratic behavior.