The couple has been dating for only six months, and not many people even knew about their courtship, the magazine reported.
But what does time matter when you're in love, right?
The "Sk8r Boi" singer isn't being shy about her relationship any longer. She retweet a congratulations post from Nickelback's Twitter account.
Lavigne's rep told People exclusively that the two rockers are definitely engaged to be married.
Lavigne, 27, and Kroeger, 37, met in February when they collaborated on a song for Lavigne's upcoming fifth studio album, the magazine said.
"A romantic relationship blossomed as they spent time writing together," a friend of Lavigne told People.
But the two didn't come forward with the news as soon as it happened. Kroeger got down on one knee for Lavigne on Aug. 8, offering the pop princess a 14-carat diamond a rock as long as she promised Kroeger to be with him "until death do us part."
"He makes her so happy," a family member told People. "Both of their families could not be more excited."
While some tweeters were confused, others wished Avril Lavigne and Chad Kroeger the best of luck.
@_Snape_ wrote, "Avril Lavigne and Chad Kroeger of Nickelback are getting married? I can't breathe, there's just too much happening. Biggest news day ever."
@Cam_Oflage posted, "Seriously how is "Avril Lavigne To Marry Chad Kroeger of Nickelback" real news & not just an unimaginative joke by a bad Canadian comic"
@mrs_zaynmalikx tweeted, "Avril Lavigne to Marry Chad Kroeger of Nickelback *cringe* what a plot twisted day"
@JordanLeeBagley said, "Avril Lavigne to Marry Chad Kroeger of Nickelback? Well he aint no skater boy"
@itsmeuna wrote, "This was suddenly, but if Avril's happy, I'm happy. Avril Lavigne to Marry Chad Kroeger of Nickelback."
@RoodGttz thought, "I think this must have been the worst birthday for Brody. Knowing that his ex Avril Lavigne to Marry Chad Kroeger of Nickelback is not cool."
Are you shocked by Avril Lavigne and Chad Kroeger of Nickelback marrying so suddenly?