Avril Lavigne Engaged to Nickelback's Chad Kroeger

Whoa, Canada!

Avril Lavigne and Nickelback frontman Chad Kroeger's relationship has been so quiet that few even knew they were dating. Now, after a six-month courtship, the Canadian rockers are engaged to be married, Lavigne's rep tells PEOPLE exclusively.

Lavigne, 27, and Kroeger, 37, first got together in February to co-write a song for Lavigne's upcoming fifth studio album.

"A romantic relationship blossomed as they spent time writing together," a Lavigne pal tells PEOPLE.

On Aug. 8, Kroeger popped the question, presenting Lavigne with a 14-carat diamond sparkler.

"He makes her so happy," a family source tells PEOPLE. "Bo...