Mila Kunis throws surprise 35th birthday bash for Ashton Kutcher

Mila Kunis threw her boyfriend Ashton Kutcher a surprise 35th birthday bash last week (begs04Feb13) at a go-kart racing center in California.

Ashton Kutcher officially turned 35 on 7 February (13), and, to celebrate the milestone, his former That '70s Show co-star invited 50 of the hunk's best friends to Go Kart World in Carson last Saturday (09Feb13) for a special party.

In addition, Mila Kunis had his favorite fast-food restaurant, Umami Burger, provide snacks for the attendees.

And it appears the group had a blast - a source tells Us Weekly magazine, "She went through so much effort to keep it a secret. He was genuinely shocked. After everyone yelled, 'Surprise!' he turned to Mila and kissed her. He was so touched. He kept looking at her and grinning (from) ear-to-ear. They had a great time."

The couple began dating last year (12) following Ashton Kutcher's split from estranged wife Demi Moore.