Christina Aguilera's boyfriend treated her to an early surprise birthday bash.

'The Voice' USA mentor turned 32 on Tuesday (18.12.12) but returned from a Christmas shopping trip last weekend to find her house decorated with balloons and filled with her friends and family.

A source told USMagazine.com that the 'Your Body' singer was completely shocked her long-term boyfriend Matthew Rutler went to so much trouble to surprise her.

The insider said the bash took place on Saturday (15.12.12) at her Beverly Hills home and was attended by 20 of her closest friends, including Nicole Richie and Blake Shelton.

The guests enjoyed a two-tiered black, pink and white cake from trendy eatery Vanilla Bakeshop.

The source said: ''Everyone was very friendly and got along well. They had a great time.''

The singer and actress met her romantic boyfriend on the set of 'Burlesque' in 2010.

The couple got together shortly after Christina ended her five-year marriage to Jordan Bratman, and a friend claims no one expected their relationship to become so serious.

The insider said: ''We thought it was going to be a quick, seat-of-your-pants romance, [but] it's turned into something special.''

A driving force behind their success is believed to be Matthew's bond with Christina and Jordan's four-year-old son Max.