Celine Dion is shocked when fan proposes in front of her, invites herself to the wedding!

Celine Dion didn't know what to do when a meet-and-greet turned into a marriage proposal over the weekend.

Before one of her residency shows in Las Vegas, Nevada, on Friday, she happily greeted her fan, Austin McMillan, and her boyfriend, Nick Janevski. McMillian tells ET that after the first photo was taken with the 48-year-old singer, Janevski "got down on one knee" and popped the question.

"I was shocked and couldn't get any words out, so Celine backed up into the curtain behind us and said, 'Are you going to say yes?'" McMillian, 24, recalls. "Celine was shocked and I was too. She was super sweet and wished us a long and happy marriage like she had with her husband [René Angélil]. Then [she] invited herself to the wedding!"

Gordon Vukovic

WATCH: Celine Dion Says Late Husband Rene Angelil Is the Only Man She Has Ever Kissed

McMillian isn't exaggerating when she says Dion was not ready to witness the marriage proposal, as her mouth dropped when Janevski, 24, took a knee. "Celine Dion is about the only person I wouldn't mind photo bombing the pictures of our proposal," the bride-to-be quipped on Instagram. "I'm still floating around in the clouds over here, feeling like it's a dream!! My heart is so happy!! What a dream come true."

"There are no words to describe this moment!" McMillian added in another photo caption. "What I thought was just going to be a special night seeing my favorite performer, turned out to be a night filled with so much happiness, surprise and celebration."

WATCH: Celine Dion and Kathie Lee Gifford Tear Up Talking About Their Late Husbands -- 'We Were Both Extremely Lucky'

Last month, Dion remembered her late husband on the one-year anniversary of his death by sharing a lovely video montage to Facebook. "Today, January 14th, it's been a year since René left us," Dion said of her husband of 21 years. "He will always be in our hearts. -Team Céline ❤."

Gordon Vukovic

Gordon Vukovic

Gordon Vukovic

Reporting by Brice Sander.

PHOTOS: Check out Celine's fun reactions at a Paris Fashion Show