During Whitesnake's performance, the band stopped the show so that Devin could call up the Sons of Anarchy actress to the stage.
"I fell in love with a very beautiful woman a few years ago, and I want to embarrass her as much as I can," Devin said, laughing.
De Mateo, along with her 7-year-old daughter Alabama and 4-year-old son Waylon -- who she shares with her ex Shooter Jennings -- came up into the spotlight where Devin shared, "I've been in love with you since the day I met you and I will for the rest of my life, and I hope that you'll marry me."
The entire, heartfelt proposal can be seen in the video below. There's some NSFW language, but it's still super sweet.
On Tuesday, Devin shared a loving pic of the happy, newly engaged couple on Instagram.
"Big Huge Thank You for all the Birthday wishes," he captioned the sweet photo. "And for all the blessings on my engagement to this kitty cat ... Much appreciated!"