Actress Jessica Biel arrives for the premiere of "Easy Virtue" in Leicester Square, London October 28, 2008. [Agencies]

Jessica Biel threw her boyfriend Justin Timberlake a surprise birthday party yesterday .

Justin - who turned 28 on Saturday? - was stunned when he arrived at Los Angeles' Hollywood Roosevelt Hotel's lavish penthouse suite to find his friends and family waiting to celebrate his special day.

A source said: "Justin was totally blown away when he walked in. He had no idea."

The 100 guests - including Justin's best friend Trace Ayala, the singer's cousins and Jessica's brothers - were treated to pizza, buffalo wings and red velvet cupcakes.

Jessica and Justin, who have been dating for over a year, looked more in love than ever at the party.

The source added to People magazine: "They held hands and relaxed. They seemed very happy together."

Justin wasn't the only celebrity to celebrate his birthday over the weekend.

Ellen DeGeneres and Portia de Rossi - who got married last August - threw a star-studded joint party at their Beverly Hills house on Saturday.

Ellen - who turned 51 on January 26 - and Portia - who was 36 on January 31 - invited Jennifer Aniston, Courteney Cox and her husband David Arquette, Drew Barrymore, Sacha Baron Cohen and Ben Stiller to help them mark their special days.

A source said: "This is their first big party together as a married couple. Ellen and Portia seem very excited to have all their friends here."

DJ Samantha Ronson played a set in the couple's backyard and was accompanied by her girlfriend Lindsay Lohan.

Guests enjoyed a lavish vegan meal.