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The One Chicago Star You Probably Forgot Played Darren Thomas On Castle

NBC's "One Chicago" franchise is a line-up of hit shows that feature literally dozens of talented actors (think Jason Beghe, Oliver Platt, and Jesse Spencer) who appear in the respective ensemble casts of "Chicago Fire," "Chicago P.D.," and "Chicago Med." With so many seasoned stars involved in this franchise's hundreds of various episodes, it's no great surprise many of them boast impressive on-screen resumés that include credits from other popular network shows. Take, for instance, "Chicago Med" actor S. Epatha Merkerson, who cut her procedural teeth on the beloved NBC series "Law & Order," or "Chicago P.D." alum Sophia Bush, who rose to prominence thanks to her star-making turn on the teen drama "One Tree Hill."

Let's also consider ABC's mystery-comedy "Castle." Airing for eight seasons from 2009 to 2016, "Castle" attracted a loyal audience with its narrative formula, pairing mystery novel writer Richard Castle (Nathan Fillion) with New York City detective Kate Beckett (Stana Katic). Initially thrown together when a killer starts reenacting murders from Castle's best-selling books, things are rough for the crime-solving duo, with Beckett resisting Castle's involvement in her cases. But, as they investigate and solve more crimes, the pair gradually develops a mutual attraction, and the show zeroes in on this opposites-attract romantic element as the series progresses.

So, with the above-noted plethora of actors to choose from, just who is the fan-favorite "One Chicago"-verse star you may have forgotten appeared as Darren Thomas in "Castle?"

Chicago Fire's Taylor Kinney plays Darren Thomas on Castle Season 4

The well-known "One Chicago" star who takes on the role of Darren Thomas in "Castle" is none other than "Chicago Fire" regular Taylor Kinney, who portrays Rescue Squad 3 truck leader Kelly Severide on the NBC drama. Kinney drops into the world of "Castle" on the Season 4, Episode 17 installment titled "Once Upon a Crime." As it turns out, this particular "Castle" episode aired in June 2012, just a few months before Kinney's debut in the pilot episode of "Chicago Fire" in October that same year (via IMDb).

On the episode, Kinney's Darren Thomas is implicated in a case involving a series of killings with a fairytale motif. One of the crimes includes a victim found dressed up as Red Riding Hood with what at first appears to be claw marks from a wild animal. Castle and Beckett first think it's possibly a wolf — as in, the Big Bad Wolf. When the mystery is ultimately unraveled, Kinney's character is cleared of the grisly murders. But, coincidentally, the actor does have another direct connection to characters who exhibit wolfish behavior in his list of past TV credits. As his IMDb profile reminds us, he plays werewolf Mason Lockwood in his 10-episode run on The CW series "The Vampire Diaries."