Kit Harington hilariously covers 'Drops of Jupiter' for 1,500th 'Tonight Show' episode

"I had a lot of thoughts when you sent me that—like, a lot," the 34-year-old British actor told Fallon after his performance. "And the sensible part of my brain, the bit that said, 'You're not a singer. You've no connection to this song. It's of no relevance to anything you're talking about on the show,' said don't do it."

"But there's a little part of my brain, the bit that gets my in trouble, that was like, 'But what if you're brilliant?'" Harington continued. "'What if it opens up whole new vistas of a career in singing?' The thing is, that 10 seconds before I started, that same little part of my brain said, 'You shouldn't have done this.'"

Harington was actually visiting the show to promote his episode of Modern Love. The Amazon Prime Video anthology series premiered its second season Friday (Aug. 13).

Along the way, Harington discussed becoming a first-time father to a six-month-old son with his wife, Rose Leslie.

"Anyone who's a parent will know you get so much advice leading up to, and it's all useless," he said. "It's all useless! It's all stuff like, 'You guys are gonna be great. You're gonna love it.' No one tells you that essentially—at first, anyway—what it is you get, like, a new roommate just dumped into your life who you've not interviewed, who doesn't know any of your house rules, breaks all your house rules, and then you fall in love with him, so you can't kick him out."

He later shared that his son loves dancing to the Beatles but only if Harington is dancing ridiculously, which he demonstrated with Fallon.

Harington also dished (very vaguely) on his forthcoming film roles in Marvel Studios' Eternals and Baby Ruby.

Watch Harington's full Tonight Show interview segment below.