The Scottish singer's breakout hit Someone You Loved rose all the way to the top of the Hot 100 after six months on the chart on Monday.

He's the first Scot to score a solo US number one since Sheena Easton's Morning Train (Nine To Five) in 1981.

"I have no clue why this piano ballad has done what it's done," said Capaldi.

"I never thought we were writing a big song here. I just wrote a song and, thankfully, people seemed to like it."

Capaldi's lovelorn ballad spent seven weeks at number one in the UK over the summer, and has also topped the charts in Canada, Ireland, Malaysia and the Czech Republic.

In the US, however, it has been a sleeper hit, taking 24 weeks to reach the summit; where it replaces Lizzo's Truth Hurts.

"I feel like America's sweetheart, at least for a moment," Capaldi told Billboard magazine. "I feel like I'm the sweetest heart in all of the US of A."

"I feel like I'm a wrestler, and I'm just walking out [to the ring] and there's an American flag, and I'm saying, 'USA! USA!' That's what I feel like, a wrestler."

The 23-year-old, who still lives with his parents, added that breaking the US meant, "I'll be able to pay the rent for the next few months!"

Other Scottish musicians to top the US single charts include Annie Lennox, Rod Stewart and Calvin Harris - however all of them did so as part of a group, or as a featured artist.