Plus: Stars send their congratulations to newlyweds DeGeneres and Portia de Rossi

Singer/songwriter Joshua Radin was elated to serenade Ellen DeGeneres and Portia de Rossi on Saturday during their private nuptials.

I cannot imagine topping that experience,” Radin told PEOPLE exclusively of his performance for DeGeneres, 50, and de Rossi, 35. “I’ve never played a wedding before, and I probably won’t again until it’s my own.

For his performance, Radin – who was hand-picked by DeGeneres as a surprise for de Rossi – sang acoustic renditions of several new tracks, including the ballad “They Bring Me To You.”

But Radin isn t the only one to share his happiness for the newlyweds: Congratulations have started flooding in. “I wish her all the best, all the happiness, all the joy that comes with that certificate in hand,” Katherine Heigl, a self-proclaimed fan of DeGeneres, said upon hearing the news.

America Fererra added that she has no advice for the couple, only well-wishes. “I’m just so happy that they get to love each other in such an official way.”

Grey’s Anatomy star T.R. Knight also sent his congrats along with his relief that same-sex marriage is now legal in California. “I happy that they re happy,” said Knight. “I m happy that they re allowed to get married.”

For more on Ellen and Portia’s wedding and exclusive personal photos, pick up the new issue of PEOPLE on newsstands Friday