The Hollywood hunk was scanning scripts during a flight before filming the pilot episode for the show, in which he played Deputy Communications Director Sam Seaborn, when he realised then-President Bill Clinton's infamous intern-turned-lover was a fellow passenger.
He took the chance to tell Lewinsky that a show focusing on the White House was heading to Tv, and insisted her fling with the Commander in Chief would not be referenced in the series.
In new U.S. nostalgia Tv show, The '90s: The Last Great Decade?, he says, "I think two or three days before we filmed The West Wing pilot, I was reading the script and studying my lines on a plane. And I got the feeling of someone watching you - you know how that can be? - and I looked up across the aisle, and it was Monica Lewinsky.
"I had this moment, I thought, 'You know what? I gotta say this to her. And I said, 'Listen, I just want you to know something. I'm about to do a show called The West Wing. It's about the presidency. I think people are going to pay a lot of attention to it. And I just want you to know we're not doing anything about... you know, so you don't need to worry.'"
The show first aired in 1999, a year after their affair led to Clinton's impeachment in 1998. He was later cleared.