United Kingdom, Sept. 29 -- Matthew McConaughey has revealed it was a question from his then four-year-old son that ultimately convinced him to marry Camila Alves.

Speaking on the Modern Wisdom podcast on Monday, the Academy Award-winning actor, 55, said his son Levi, now 17, once asked why his mother, 42, did not share the same surname as his father -as at the time, the family had not yet formalised their union.

Matthew said: "I'm going through my head, 'You're f****** four, dude'.

"I sat there. I was like, 'It's a great question, but I mean, we're not married. When you get married, you switch your name'."

Matthew recalled Levi listened intently before asking his father whether he was afraid of getting married.

He added: "I was like...