He told the Herald that he was a bit shocked when he first read the scripts for series three.
"It was strange, because Fran has done a complete U-turn this season," he said. "It took a while to get my head around that curve. To understand where he was coming from.
"Fran and Nidge have almost swapped places. Last season Nidge was the comic relief and now Fran is bringing some of that to the series."
Peter explains: "Fran was spiteful in the last series. He was a real animal with no morals. Arranging dog fights and all that. But he's calmed down in this series."
The Leopardstown native says that he thinks Fran's stint behind bars has changed his character. "I think he sees things differently. He's just come out of jail and he's free -- so he's going to be in good form. He's got no money, he's starting from scratch and he has nothing to prove."
He adds: "It's very dark comedy but you really need those moments of relief in a series this heavy."
But Peter says it's nice to play a character with so much variety. "It's great when the writers mix it up. Things can get boring and tedious if you're playing a character that aggressive all the time. So it's great taking him in a different direction."
And Fran certainly seems to be enjoying himself in the upcoming episode. He joins Nidge and Darren as they visit the brothel where Debbie works. The guys knock back pints as they watch girls dance.
Peter seems to be a natural when it comes to playing drunken louts.
"Yeah that's method acting," he joked. "Seriously though, it's really tough playing those scenes. A lot of them are filmed first thing in the day so you've got to work hard to make it convincing. It's hard to find that energy and create that sense of fun that early in the morning."
Nearly one million viewers tuned in to the opening episode of Love/Hate's third series. RTE were hit with more than 30 complaints but Peter said that the reaction he has received has been overwhelmingly positive. "The reactions been great. I've had people saying 'coolaboola' to me and everything." In last week's episode Fran brought back the uncool phrase 'coolaboola'. The gangster uttered the phrase after burying Git's body in the back of his garden with a JCB.
Peter said that he had been anxious what the reaction would be. "The show deals with a lot of issues and you do get nervous watching it. You start thinking 'what's my dad going to think of this?', that sort of thing.
"After the episode went out on Sunday night, I rang Killian Scott and we just had a chat to calm down."
In tomorrow night's episode Nidge tries to convince Dano that he had nothing to do with his father's disappearance. But a scapegoat will have to be found so Nidge turns to ever-faithful Darren for help.
"It gets more intense," Peter said. "I can't say too much but you'll have to watch on Sunday night to find out."