Wilmer Valderrama‘s birthday party was a mini That ’70s Show reunion!
When Valderrama arrived, he was surprised by the large group of friends there to join him.
“He was laughing and saying that he had expected a quiet dinner,” a source tells PEOPLE.
Kutcher, 36, and Kunis, 31, “looked cute” as they shared a family-style Thai dinner and enjoyed drinks throughout the evening.
When it came time to sing “Happy Birthday,” Valderrama’s girlfriend Demi Lovato, who planned the surprise party, presented the birthday boy with a personalized cake.
They clapped and cheered when Wilmer blew out the candles, the source says of the new parents. “They acted very down to earth.”
After Valderrama blew out the candles, Kutcher led the guests in a rendition of “For He’s a Jolly Good Fellow.”
“Ashton and Mila looked cute,” the source says. “They seemed to have the best time.”
• Reporting by PERNILLA CEDENHEIM