Serenaded by Sia! More Details Inside Jen and Justin's Wedding

Guests also sang 'Happy Birthday' to Justin Theroux, who turns 44 on Monday

Photo: Getty (2)

Jennifer Aniston and Justin Theroux were treated to their own private concert as Australian singer Sia performed after the couple tied the knot at their romantic backyard ceremony on Wednesday in L.A.

Guests who had been told they were attending a birthday party for Theroux, began arriving around 4:30 p.m. and were checked in at a table as they entered the couple’s estate. According to a source, the wedding ceremony was held inside the house and Aniston, 46, came outside around 9 p.m. when the reception was going strong. Music included Michael Jackson’s “Billy Jean” and even a rousing rendition of “Happy Birthday” for Theroux, who will turn 44 on Monday.

Shortly before midnight, guests applauded as Sia performed her hit “Chandelier.” One early clue she might be involved in Aniston’s wedding: Sia was spotted in May having dinner in L.A. with Aniston and her BFF Courteney Cox, who celebrated alongside the newlyweds all night. The singer left the wedding around 1 a.m., but the festivities continued into the wee morning hours. “At 2 a.m., the music was still pretty loud,” adds the source.

On Thursday, the newlyweds were spotted taking off on a private jet to Bora Bora for their honeymoon. A source tells PEOPLE the couple invited a few pals, including Chelsea Handler, to join them because they wanted the celebration to continue.