Lindsay Celebrates Her Birthday with Sam Ronson

Capping off a week that saw the shocking revelation of the existence of secret, 13-year-old half-sister, Lindsay Lohan celebrated her 22nd birthday Wednesday night in a rather modest fashion for the infamous party girl.

The location for the special event was celeb-friendly haunt Teddy's at the Hollywood Roosevelt Hotel, and the young actress, decked out in a fuschia mini-dress, was joined for the prom-themed affair by her mother Dina Lohan and tuxedo-wearing gal-pal Samantha Ronson.

The room was decorated like something straight out of a 1980s teen flick, with red, silver, baby-blue and light-pink balloons, palm tree banners and "Happy Birthday" napkins on the bar. The birthday girl's table was filled with cupcakes, including one with a tiara especially for Linds.

La Lohan sipped on cans of Red Bull through the night while DJ AM spun tunes for the crowd of around 50 guests.

Just before midnight, everyone gathered to sing "Happy Birthday" to the actress, who was presented with a large cake featuring the famous photo of Marilyn Monroe from the Seven Year Itch with her dress billowing up around her.

After blowing out the candles, Lindsay thanked everyone for coming out. Then it was time for Sam to jump into the DJ booth and take command of the turntables for the last hour of the party with Linds at her side until the party came to an end shortly after 1 am.