"We're only getting older, baby."

It's a sentiment One Direction sang about on 2012's "Live While We're Young," where they celebrated the moment because they didn't know what would happen tomorrow.

Two years later (eons in boy band years), the lads are still preaching that same philosophy, except this time, it's softer, sweeter and a little more genuine, and they throw the party-hardy attitude away. With the release of their fourth album, FOUR, on Monday, they've come to admit that they're not, well, kids anymore. And that's OK.

In their second single, "Night Changes," out Friday (November 14), the guys sing about how much can change in an instant. While they remain vague about the circumstances, one thing will never change: "me and you," they sing sweetly.

MTV News recently caught up with 1D songwriter and opening tour act Jamie Scott, who co-wrote "Night Changes," and he gave us the story behind the track.

“One of the songs on the record came from myself falling out with Julian Bunetta and John Ryan,” Scott told us, explaining how he writes and produces with 1D, Bunetta and Ryan in his basement studio. Occasionally, he has to step out to care for his kids, but the others stay and vibe.

“These guys just work through the night," he said. "And one night, I came down to the studio, and three songs that I thought were sounding amazing when I left had been changed drastically through the night... The song is nothing about that, but the idea and the word came from me coming in the morning, because you get a bit delirious and you never quite know what you’re doing, but it was fine and all was resolved and we had a great song title.”