Avril Lavigne's engagement to Nickelback's Chad Kroeger came out of nowhere last summer, but things seem to be going well.

They talked to On the Air With Ryan Seacrest to promote her new song, "Here's to Never Growing Up," and Chad revealed how their relationship grew. “I think it evolved into this wonderful thing," Chad, 38, said. "When you’re sitting there, singing across from somebody into the microphone and singing love songs and you start developing these feelings for that person, and it just blossomed into this thing and last summer we started dating and I didn’t take long, I got down on one knee."

They had only been dating a month before Chad proposed, and Avril, 28, shared the story.

Credit: Chelsea Lauren/Getty Images Photo: Avril Lavigne at Her Abbey Dawn Show at New York Fashion Week on September 10, 2012

“The only thing that was weird was we usually go to the studio together and he had gone before me," Avril said. "And I have been making this scrapbook of my time in the studio with a Polaroid camera and the only thing that was weird was I walked into the studio and he was putting a picture into the book and I was like ‘What is he doing?’…And all of a sudden I walk over and he had taken a photo of himself holding the ring box and put the Polaroid in my scrapbook and because I had stickers everywhere he put in ‘Will you marry me?’ It was really romantic."

Avril told Ryan there's a theme to their wedding, and it will be "quite spectacular" and "pretty big" — but even Chad doesn't know all the details yet, and they're not sharing the wedding date. Head here for more. Good luck to them!

Source: On the Air With Ryan Seacrest