Killian, who plays Tommy in the hit RTE series, thinks Tom Vaughan-Lawlor, who plays Nidge, will be an unlikely heart-throb in the fourth series. "I think Nidge is very sexy," said Killian (27).
"I think Nidge is going to be the new heartthrob on Love/ Hate, that hairstyle really gets women going.
"He's been an understated sex symbol for a while but I think he'll come to the fore now Robbie is no longer in the series," he joked.
"Seriously though, I think Robbie will forever remain the ultimate heartthrob of the series."
Killian was quick to brush aside suggestions that he may pick up Robert Sheehan's mantle. "No, no. My money is definitely on Tom Vaughan-Lawlor," he laughed.
Killian's character spent the majority of the last season getting up close and personal with an assortment of women, including prostitute Debbie and the wife of provo leader Dano, but Killian says steamy sex scenes don't bother him in the slightest.
"There's always an inherent awkwardness to that sort of thing. But it doesn't really matter to me at all personally. But I went to a pretty weird acting school," he said.
"It's just sort of mechanical rather than anything else," he said. "It might seem sexy when you watch it back but on the day it's nothing but mechanics.
"You're just going through the motions and figuring out the logistics of it all.
"In those situations, it's all about the other person and making sure they are comfortable and hopefully they feel at ease. But it doesn't bother me.
"You've got to try and have as few inhibitions as possible when you're an actor."
In the last season, Tommy was left hospitalised and close to death after Nidge battered him. And Killian says he's unsure if his character will return to the series or wake from his coma.
"I don't really know what my chances of survival are, it was a pretty serious head injury. Stuart [Carolan -- the writer] makes those decisions.
"I trust him completely but I have nothing to do with the script process.
"But I hope I get a chance to sport that awful haircut again," he said.
In the meantime Killian is busy working with the Jameson Dublin International Film Festival which starts on February 14.
"It's great to be part of such an exciting festival," he said. "Danny DeVito and Tim Roth will be here in Dublin. It's going to be amazing."