Lavigne played a secret show produced by Talent Resources and CEO Mike Heller at The Viper Room in West Hollywood on Thursday to over 2,000 people – including Jack Osbourne – and Kroeger couldn't have been more proud.
"Chad was extremely supportive throughout the evening," an onlooker tells PEOPLE. "He was rocking out to Avril's performance, dancing and singing along like no one was watching. He was solely focused on Avril."
As the "Here's to Never Growing Up" singer closed out the show, she thanked the crowd and then went to give Kroeger a "big hug and kiss." "They were both glowing," the source adds.
When they couple exited the venue, they stopped to sign autographs, but Kroeger made sure his bride-to-be was the main attraction.
"Chad didn't take too many [photos] or sign too many autographs because it was Avril's night and her time to shine. You could tell she appreciated him respecting that," says the source.
– Melody Chiu