ET's Ashley Crossan caught up with the actors at the movie's premiere in Los Angeles, California, on Wednesday, and Hunnam explained why he rarely spoke to his co-star when the cameras weren't rolling.
"There was something really exciting about the idea of not knowing someone, just letting a relationship exist exclusively on the screen," the 36-year-old actor noted. "So, I had decided that I wanted to do that, but sometimes that can be alienating, and [can] put another actor off of their work and I don't want to be that selfish."
Hunnam added that Pattinson also wasn't super friendly towards him either. "I started playing this game with Rob and he just started playing it right back," he said. "I think we both really understood what we were doing and there was no real contention or beef between us -- we were just playing the game."
The Sons of Anarchy star further insisted that he has no ill will towards Pattinson. "It's nice actually to come out of that fog of the production and see that he's a lovely guy," Hunnam continued. "I can actually enjoy having a drink with him now and a hang."
ET also spoke with Pattinson about working with Hunnam. "I didn't ignore him," the 30-year-old actor said before adding, "Well, whatever, maybe... I thought he was ignoring me."
"I dont know. It was just the two of us in the hotel," Pattinson noted.
In The Lost City of Z, hitting theaters on April 21, Hunnam portrays British explorer Percy Fawcett, who disappeared in 1925 while on a search for a mythical city that he believed existed in the Amazon. Pattinson plays fellow explorer Henry Costing while Sienna Miller portrays Percy's wife, Nina Fawcett, and Tom Holland is the couple's son, Jack Fawcett.
Hunnam turns 37 just a couple of weeks before the release of the movie and told ET that his upcoming birthday "feels significant" because he only has three more years until he's 40. "Forty feels really significant for some reason," he said. "It's just a number like any other, but I gotta start having some kids, get married, start being sensible in my life."