Charlie Hunnam admits he hasn't exactly been the ideal boyfriend.
While filming The Lost City of Z in Colombia last year, the 36-year-old actor went full-on Method, giving his girlfriend of 11 years, Morgana McNelis, the silent treatment for five months.
WATCH: Charlie Hunnam Strips Down and Opens Up About Life After 'Sons of Anarchy'
"We went to Colombia, and the mail system doesn't really work very well. It's completely unreliable," the British heartthrob, who says he promised McNelis a letter a day, told Entertainment Weekly. "I received a letter from her, and I realized that from the tone of it and [the] things she was saying that she hadn't received the two letters that I sent before."
Upon discovering that his first few letters didn't make their way to McNelis, Hunnam decided to stop writing altogether. Instead, he fully tapped into his character, Percival Fawcett, a British explorer who went missing in search of an ancient city in the Amazon in the 1920s. Hunnam said the lack of communication gave him a clearer perception of the absentee father.
"One of the things that [director James Gray] and I felt strongly that we wanted to explore in the film," he explained, "was the conflict between family life and the exterior demands that are made on us and the social and economic demands that we all need to deal with in life, being balanced or in conflict with the internal drive, to be the people we want to be and achieve the things that we want to achieve."
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Hunnam confessed that he was well aware his behavior "obviously makes me sound like a total bastard, appropriately so," but said he "was very apologetic" when he finally returned home. To make up for his absence, he came back with a shiny new present for McNelis!
"I had the benefit of shooting in Colombia, where they have rather lovely and somewhat cheap emeralds," Hunnam dished. "My girlfriend is a jewelry designer, so I was able to come back with an appropriately sized gift. It didn't remedy all of the trouble I was in, but it got me halfway there."
Back in July, ET caught up with Hunnam at San Diego Comic-Con, where he fessed up to taking a bike from the Sons of Anarchy set after the series wrapped filming in October 2014.
WATCH: Charlie Hunnam Cops to Stealing a Bike From 'Sons of Anarchy' Set
"It was like one of those weird things that like a kid does," Hunnam explained. "I stole it, but I've never used it."
Hear more in the video below!