The CW has confirmed the first crossover between Arrow and The Flash.

According to TV Line, Robert Knepper will reprise his role as William Tockman (aka The Clock King) on Episode 7 of The Flash Season 1.

The villain appeared on the Arrow Season 2 installment “Time of Death” and will be the first antagonist to stalk both Starling City and Central City.

Executive Producer Andrew Kreisberg, meanwhile, tells TV Line that Barry Allen will face a “real challenge” on the installment, as a “new enemy” will be featured on the same episode as The Clock King.

The identity of that second villain is unknown at this time.

The Flash speeds into our lives on Tuesday, October 7 at 8/7c.

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.