"So It Begins." In tonight's episode of "Arrow," "Expendables" star Dolph Lundgren will make his debut as an ominous figure from Oliver Queen's past. As Konstantin Kovar, Lundgren plays Oliver's chief antagonist in the series' Season 5 flashbacks. However, according to Stephen Amell, their relationship was a little more amicable behind the scenes.

"Yeah, he is [a legend]! It's interesting, watching someone that has sort of cut their teeth in film walk onto a 23-episode-a-year television show with 14-hour days, because he just moves at his own pace," Amell recalled during a brief break between filming scenes. "It's not indulgent; when he came to set, he knew his stuff, not that I expected anything less. He was very respectful. He asked a lot of questions. He had clearly done his homework. But, you know, Dolph moves the way that he moves!"

"He's very thoughtful and contemplates his lines and he has been great so far, but it's a real change of pace," he continued. "I do think it would have been a missed opportunity in the last year of these flashbacks to not have a really worthy adversary. We found that in Dolph, which is why he'll be around for a while. It's been a blast to work with him. It's been awesome."

Echo Kellum, who plays Curtis Holt, also weighed in on Lundgren's presence on set -- even though he doesn't share any scenes with him and has not yet officially met him. "Man, I did not get to meet him! And I really wanted to because I was a big 'He-Man' fan and 'Rocky 4' fan, obviously," he shared.

Nevertheless, Kellum did get a brush of his fame, albeit in an unexpected way. "One time I was going into my trailer and then I open up the drawer and there was this envelope in there. I was like, 'What is this?' And I open it up, and it's all these cool behind-the-scenes 'Rocky 4' pictures. So I was like, 'Dolph Lundgren was in here!'" he shared. "I quickly put the envelope back. I was like, 'I better not touch this because he could kick my ass.' But yeah, that was a really cool moment. Holy crap! These intimate, behind-the-scenes pictures of him fighting and all this stuff like that… it was really cool. I would love to meet him… I was a huge fan of his growing up as a kid."

Starring Stephen Amell as the Emerald Archer, "Arrow" airs Wednesdays at 8 pm ET/PT on The CW. The series also stars Emily Bett Rickards, David Ramsey, John Barrowman, Willa Holland and more.