The announcement was made by Amell today during their joint appearance at Heroes & Villains FanFest in Secaucus, New Jersey. "I'm so fired up," the actor said.
No details were revealed about the role, but TVLine reports that Rhodes -- perhaps better known as Stardust -- will appear in the third episode of Season 5.
"You can probably expect Stephen and I to get into another fight," Rhodes teased.
Watch video from their convention appearance below. "Arrow" returns Wednesday, Oct. 5, on The CW.