'The Expendables 4' producers are pleased with the new blood in the franchise.

Megan Fox and 50 Cent have joined action legends Sylvester Stallone and Jason Statham in the latest movie in the action series and producer Kevin King Templeton felt it was necessary to add some new faces in the flick.

Kevin told Screen Rant: "Each movie has different characters in there. In order to evolve, you can't reinvent the wheel, but you have to freshen it up.

"You have to put new characters in there, but these characters have to fit, and they have to be right. It was kind of an extensive casting process, but I'm hoping we got the right balance."

The producer continued: "It was more a Christmas-centric movie, (and) we needed a foil for Jason, so Megan was cast in it. We thought the chemistry was perfect between the two of them, which is why we cast her.

"50 (Cent) added some much-needed blood to the back team. You don't reinvent the wheel, but you definitely polish the tires and give it a new coat."

Templeton revealed that the cast and crew were determined to make sure that the movie was a "bread and butter" action picture.

He said: "The movies are – we're not superheroes. We're not Marvel; no one throws a cape on and flies through the air. It's old-fashioned action, and that was the main thing, when we were developing, everyone agreed that we needed to stick to.

"That's what started it. That's the bread and butter of this franchise. That's the lifeblood of it, so we knew what we were getting into. It wasn't a question of, 'We have to stay true to it.' We always had that philosophy for this. It never changed, and I don't think it will."