The handsome star, who played SAM SEABORN in the White House drama until 2003, was working out when a television news report announced his character's exit.
Lowe, 41, says, "I was in the gym working out and it was on CNN. I am on the treadmill and everyone on the 10 treadmills beside me said, 'Why?'
"My stock answer is that there's an art to knowing when to leave the party. "Every great long-running show has great years.
"If there's an ER with George Clooney in it, it's going to be great. The West Wing experience was like being in THE Beatles. It's still one of the best shows, but when (writer/creator) Aaron Sorkin left, it wasn't going to be the same. And the truth is, I missed Aaron's dialogue."