Songwriter to the stars Tobias Jesso Jr. got his big break in 2015 when Adele discovered him on YouTube and enlisted him to co-write a track for her album 25 -- he has kept busy ever since. Most recently, he's added Florence + The Machine, Pink, Charlie Puth and Niall Horan to his quickly growing resume. "I've been really lucky," he says, "because Adele opened the door for me to work with these kind of artists."

He recalls what it was like to work with Welch, Pink Puth and Horan some of their biggest tracks from the past year.

FLORENCE + THE MACHINE, “Hunger,” "Grace," "The End Of Love" (High As Hope)

“I think she's a genius. She would start singing words from her diary in her Florence scale -- which I couldn't even map -- and I'd be like, ‘This is going in a good direction.’ She’d be like, ‘No, we just recorded it. It's done.’ It's funny because all of her fans are like, ‘She's a mother goddess queen of nature and channels whatever spirit god.’ That's actually true.”

PINK, “You Get My Love” (Beautiful Trauma)

“Her voice is nuts. The first [of two days] we worked together we were writing a little bit, talking a little bit, and then we started on a song where she went super high and we were just like, ‘Holy shit, like let's take it there.’ I think we broke the scale on that one.”

CHARLIE PUTH, “If You Leave Me Now” (Voicenotes)

“Charlie Puth is a savant. And it's funny because Florence comes from this very ethereal, magical fairyland with mermaids in it and Charlie comes from this complete polar opposite place of understanding music theory like the Matrix. He decides what he wants and he just makes it -- it's like he knows the recipe for every song.”

NIALL HORAN, "Slow Hands" (Flicker)

"When artists are trying to find their sound, they take a couple random shots in the dark with other writers. I was asked to be one of the shots in the dark. 'Slow Hands' took almost no time to write. I was really stoked on the vocals -- he's got a great voice. He was signing it in the back [of the studio], which is always just amazing to have the artist there, writing with you and singing it as you go."

A version of this article originally appeared in the July 21 issue of Billboard.