The pop star marries Kevin Federline in L.A., their rep confirms to PEOPLE

Britney Spears, 22, and Kevin Federline, 26, said “I do” in a surprise ceremony Saturday evening in a leafy neighborhood in Studio City, Calif., their rep tells PEOPLE magazine.

Some 20 friends and family members – including Spears’s mother, Lynne, and sister, Jamie Lynn – were present at what was billed as an engagement party but turned into a wedding. Britney wore a white dress and Kevin a black tuxedo as the couple exchanged vows.

The ceremony happened almost a month before their planned Oct. 16 wedding, which was to take place at the luxurious Bacara Resort in Santa Barbara.

As a helicopter hovered over the Studio City house in the dark, neighbors took to the streets in a spontaneous block party.

Spears had a bachelorette party Friday night, then visited a spa early Saturday. Guests were shuttled to the wedding in vans from a Santa Monica hotel. After the nuptials, the bride and groom left in a black SUV.

Take a look at Britney and Kevin’s romance in photos.