The Hunger Games star and his wife Laura Haddock welcomed their first child, a son, in December (15), and he admits the family transition has been truly life-altering.

"I always thought, naively, that I knew what it would be like," he told People Now. "I always thought that I’d understand, (but when he was born), it’s like another level of love that you’ve never experienced before, you can’t describe to someone unless (they’re) in it."

The 29-year-old has been juggling fatherhood with his rocketing career, and he is currently busy promoting his new movie Me Before You, but Sam insists he wouldn't change a thing about his life right now and loves any snatched moments he gets with his son while he's working.

“Of course it’s hard, (but) it’s all worth it,” he said. “The rewards are just endless. He’s literally the best thing that’s ever happened to me.”

Thankfully Sam will finish promoting the movie, which also stars Game of Thrones actress Emilia Clarke, just before Father's Day (19June16), allowing him some quality time with Laura and their little boy.

"I will have a bit of family time," he said. "I don’t know what to expect, I have no expectations. I’ve never had that to look forward to before.”

Sam and Laura tied the knot in 2013 and confirmed they were set to become parents when Laura debuted her baby bump on the red carpet at the London premiere of The Hunger Games: Mockingjay - Part 2 in November (15).