Kellan Lutz has revealed he had to change Tarzan's famous cry for his new movie as the original call is trademarked.
The Twilight hunk plays the king of the jungle in a new motion capture animation of the film. But the 29-year-old could not re-enact the primal cry made famous in original Tarzan movies starring Johnny Weissmuller as the rights are owned by the estate of Tarzan creator Edgar Rice Burroughs.
Kellan said: "Everyone knows the Tarzan cry, but what I didn't know was that we weren't going to be doing it the same because it's trademarked. So we had to change it a little bit.
"So for about a month and a half of shooting we didn't have the specific cry nailed down. And then on one of the last days they finally perfected the one that they wanted and they were like, 'here this is what it is, listen to it.' And then I only did it one time that I did it. And I don't remember it. It's very similar, but we couldn't do it just the same."
The Hollywood heartthrob also admitted he ended up aching after learning to walk and run on all-fours like an ape.
Kellan admitted: "I didn't realise how difficult it was gonna be. I went to the zoo and studied the movements of apes and chimpanzees, studied the vocal calls they have, their language.
"Every animal walks in a distinct different way. Humans we lead by our chin or our stomach or our chest, we pull out from the heels, push off with our toes.
And Tarzan is such a flexible, athletic... he's a bit of a ballerina in that sense because he's so graceful. So I had to change my walking movement to more like boxer stance, where you're always on your toes ready to pounce, ready for action.
"I loved it but I've never been more sore, especially running on all fours I'm not super flexible, I should have done more yoga growing up!"
Tarzan is released in cinemas on Friday May 2.