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. "Both of their families could not be more excited."

It will be Kroeger's first trip down the aisle, and the second marriage for Lavigne, who split from Sum 41 frontman Deryck Whibley in 2009. She had also dated Brody Jenner.

For an exclusive engagement photo plus more on Lavigne's stunning ring, check out this week's issue of PEOPLE, on newsstands Friday