Christina Aguilera's relationship with Matthew Rutler is still going strong.

The singer has been dating the Burlesque set assistant since late 2010 following her split from ex-husband Jordan Bratman.

And sources have told Us Weekly that the romance has surprised all of their friends because it has "turned into something special."

"We thought it was going to be a quick, seat-of-your-pants romance," the insider told the publication. "It's turned into something special."

Matthew has apparently been eager to please the singer by taking a particular interest in her four-year-old son Max.

"He recently surprised them by taking them to Cirque du Soleil's Iris show," the pal said. "They had a blast."

Christina, 31, also threw a birthday party for Matthew recently to celebrate him turning 27.

"There were about fifty people there," a partygoer said. "It was intimate, and low-key. Matt and Christina were super affectionate."

Although the powerhouse singer has come under scrutiny for her weight increase recently, Matthew apparently thinks she is beautiful whatever size she is.

"Matt is happy with the way she looks, however it is," the insider added. "Even when she was looking heavier, he would always say, She looks gorgeous to me.'"