There's trouble on the horizon for "DC's Legends of Tomorrow." Just a few episodes ago, Professor Stein and Jefferson "Jax" Jackson stumbled upon Rip Hunter's secret room aboard the Waverider. In it, they encountered not only a stash of weapons, but a dire message from the Flash's future. However, the show hasn't revealed many details about what that message is -- and it won't, at least until the big "Invasion!" crossover between "Legends," "The Flash," "Arrow" and "Supergirl."

During a set visit, Victor Garber -- who plays Martin Stein, one half of Firestorm -- told CBR and other reporters that Barry Allen would learn of this future message in the big "Arrow"-verse crossover.

Asked how his character will continue to deal with this secret message from Barry's future, Garber said, "It sort of comes out in dribs and drabs. It's a big mystery and a big deal. It's a spoiler if I give you too much information, but it's just part of the whole mystery of time travel and the fact that this is coming from Barry years later and then when he finds out -- and that all happens in the crossover, so it just sort of unfolds as these things do on these shows, and lots of things occur in that time period."

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Though he couldn't reveal too much information about this scene, Garber did address whether or not the burden of keeping this secret will help strengthen Jax and Stein's bond. "Well, yes and no," he shared. "I mean, Stein is saying, 'We can't tell them' and Jax is saying, 'Why can't we?' It's kind of like a father and son: some days it's good and some days you just want to say, 'How did you become my child?' which is also -- for me, as an actor -- what's fun about doing it. First of all, [Franz Drameh] is a brilliant actor and I love working with him, and we have a really good time together, so it continues to be that and hopefully more dimensional. I mean, like everything, it changes, and -- if it stayed the same -- we'd be off the air, frankly."

Airing Thursdays at 8 pm ET/PT on The CW, "DC's Legends of Tomorrow" stars Arthur Darvill as Rip Hunter, Brandon Routh as the Atom, Victor Garber and Franz Drameh as Firestorm, Caity Lotz as White Canary, Maisie Richardson-Seller as Vixen, Dominic Purcell as Heatwave and Nick Zano as Citizen Steel.