There is a reference to Marc Guggenheim's upcoming Netflix series Trollhunters in an upcoming episode of DC's Legends of Tomorrow -- and that won't be the first time he's dropped one into one of his CW/DC shows.

The executive producer, who also works on Arrow and Vixen, told ComicBook.com that he actually planted an Easter egg in a season 4 episode of Arrow.

"Episode 2.11 of Legends, if everything goes according to plan, will feature a little bit of a Trollhunters Easter egg, and actually, Arrow season 4 included a Trollhunters Easter egg," Guggenheim told ComicBook.com. "There's something interesting about writing an Easter egg for a show that nobody's seen yet into your existing show, but I guess I'm just unusual that way."

Of course, by the time Legends airs its eleventh episode of the season, audiences will have had an opporutnity to see Trollhunters, which debuts on Netflix in two weeks. The show's first season will be available all at once on December 23.

Of course, without having yet seen Trollhunters, it's impossible to know just what Guggenheim might have planet on Arrow next year. It seems likely that we'll have to dig around in the season 4 episodes -- especially those where Felicity was dealing with other hackers, and so "troll" jokes might have popped up -- to look for what it was.

Trollhunters centers on a young man who is forced to take up the mantle of Trollhunter, the person responsible for ensuring the the balance of power between humanity and trolls remains intact, after his predecessor is killed and the "Trollhunter amulet" falls to him. It stars Anton Yelchin, Charlie Saxton, Kelsey Grammer, Ron Perlman, and Steven Yeun.

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DC's Legends of Tomorrow airs Thursday nights at 8 p.m. ET/PT on The CW. The show's midseason finale airs tonight.

DC's Legends of Tomorrow airs Thursday nights at 8 p.m. ET/PT on The CW. The midseason finale, titled "The Chicago Way," debuts tonight and new episodes will return the last week in January.

Trollhunters will premiere its first season on Netflix on December 23, 2016.