The CW's "Crisis on Infinite Earths" crossover has added its newest cast member -- and it's not one that fans were expecting. According to a new report from TV Insider, Osric Chau has been cast in the recurring role of Ryan Choi in the Arrowverse's upcoming crossover event, which will involve Arrow, The Flash, Supergirl, Legends of Tomorrow, and Batwoman. Chau is known for his fan-favorite role as Kevin Tran on Supernatural, as well as appearances on Kings of Con and Dirk Gently's Holistic Detective Agency.

Choi is described as a "physics professor at Ivy Tow University", whose seemingly-normal life is changed when he "learns he has a pivotal role to play" in the upcoming Crisis. This fits pretty closely with the character's origin in the comics, which leads to him being mentored by Ray Palmer, and eventually taking over the role of The Atom. The character, who was initially co-created by Gail Simone and Grant Morrison, has become a fan-favorite, appearing in Batman: The Brave and the Bold, Injustice 2, and a deleted scene in Justice League.

To an extent, the Arrowverse has been setting up Ryan Choi for several years now, as Ray Palmer (Brandon Routh) taught at Ivy Town partway through Season 1 of Legends of Tomorrow. Ryan was then mentioned by name in The Flash's Season 5 premiere, as the scientist in the future who engineers Barry Allen's Flash ring and costume.

Given the news that Routh will be leaving Legends midway through the upcoming fifth season, the notion that Ryan is suddenly appearing in the Arrowverse is certainly interesting. Whether or not Chau will end up reprising the character in Legends - as The Atom or otherwise - will remain to be seen.

Chau joins a pretty stacked list of guest-stars for "Crisis", including characters from Black Lightning, Smallville stars Tom Welling and Erica Durance, prolific Batman voice actor Kevin Conroy, and legendary Robin actor Burt Ward.

“Basically, we’re gonna begin — this is an exclusive — we’re gonna begin the way Crisis on Infinite Earths the comic begins, which is the destruction of various parallel universes. And the goal is for us to adapt key moments from the comic, those seminal moments,” Arrow producer Marc Guggenheim told ComicBook.com earlier this summer.

"Yesterday I pitched to the network what the story was going to be and the best part of the pitch, we have a board that DC made up for me, which is covers from key issues of Crisis on Infinite Earths." Guggenheim continued. "And we’re like, ‘We’re gonna do our version of this, we’re gonna do our version of this, we’re gonna do our version of this.’ Our goal is, the thing we’ve been saying, is we’re going to make a list of a 100 cool things that we want to do. And even if we only get to do 50, we’re still doing 50 cool things... This needs to be special. This is the Holy Grail of DC comic book stories, in my opinion, and we cannot screw this up.”

Are you excited to see Ryan Choi join "Crisis on Infinite Earths"? Share your thoughts with us in the comments below!

"Crisis on Infinite Earths" will begin with Supergirl on Sunday, December 8th at 8/7c.