According to People, Sun, 35, got down on one knee on March 27 while the pair was on a romantic trip to Paris.
"It was the most perfect, romantic proposal I could ever ask for," Lavigne, 37, gushed to the publication. "We were in Paris on a boat in the Seine River. We had a violin player, champagne and roses. It felt like time stood still, and it was just the two of us in the moment."
The "Complicated" singer also shared the news with a series of snaps to her Instagram page, including a photo of the giant heart-shaped rock on her left hand, which apparently has an adorable meaning behind it.
"It has the words 'Hi Icon' engraved in it, which were the first words he ever said to me," Lavigne revealed to the outlet. "And it has Mod + Avril on the inside. He knew from the very beginning I wanted a heart shaped diamond because on the day we met, we had matching heart shaped paved rings on. We've worn them every day since, so its only fitting to have a heart-shaped engagement ring. I love it so much."
Even though the "Girlfriend" rocker — who was previously married to Deryck Whibley and Chad Kroeger — said the proposal in the City of Love "was a total surprise," she knew from day one of their relationship that Sun was her soulmate.
"I knew we had a very strong unstoppable connection from the first week of writing and working together in the studio. Immediately," she maintained of her soon-to-be hubby. "He made every day better. It was like I had known him forever. As time went on, things kept getting better, and it felt incredibly natural."
"I look forward to having fun, creating, working together, touring together, growing together," the "Bite Me" singer said of the fellow musician — who she has already collaborated with on her newly-released album, Love Sux. "It feels good to have someone who can help celebrate the good times, hold you through the tough ones, and be there for all the moments in between."
Sun also shared the sweet photos of their special day in Paris to his Instagram page, seemingly echoing his future wifey in saying: "The day we met I knew you were the one."
"Together forever til our days are done. I had a dream where I proposed in paris. I pulled out a ring + asked you to wear it. I was on one knee as I looked in your eyes," he captioned the swoon-worthy pics. "You're too beautiful for my words to describe. I grabbed your hand + took one last breath…I said "will you marry me?" + she said 'yes.' I love you Avril ❤️."