Matthew McConaughey is "selfishly" faithful to his wife Camila Alves because he never wants to see another man fall under her "spell".
The Dallas Buyers Club star began dating Camila in 2006 and he remembers falling in love at first sight the moment the model and designer walked into the room.
"I had a time in my life when I was fine going from here to there, bam-bam-bam - healthy, fluent, single years...," he told Playboy magazine. "When I saw the woman who is now my wife, I was at a club making margaritas at my table with friends. When she walked in wearing this aqua dress, I went, 'Whoa, what is that...?'"
The couple wed in 2012 and three children later, Matthew admits the Brazilian beauty has him firmly under her thumb - and he wouldn't have it any other way.
"I have been very faithful with my wife, very selfishly," he said. "I like being under her spell. I don't want to break that spell."
Matthew also opened up about the first time his father Jim sat him down to discuss sex as a child in the Playboy expose, revealing he had a rather unconventional approach to teaching his son life lessons.
"He goes, 'Hey, buddy, drop your pants. Let's see what you got...'," he recalled. "It was a man-to-man, son-to-dad talk. It was really cool and kind of took taboos off things."
Jim died in 1992 while "making love" to Matthew's mother Mary.
While the actor opens up about that candid moment, he insists he'll name name the girl he lost his virginity to around the age of 15 or 16.
"It's a great story but one I'm going to keep for myself," he teased.