Federer tweeted the news Tuesday, saying, "Mirka and I are so incredibly happy to share that Leo and Lenny were born this evening!"
The twin boys join older sisters Charlene Riva and Myla Rose, who were born back in July 2009.
Most fans were clued in on the fact that Federer was about to become a dad again, thanks to his Christmas Eve tweet, which announced that he and his wife were adding to their brood. The news of twins, however, is definitely a surprise. It means fans will now have to wait a bit before they see Federer back on the court, since the tennis star revealed he's taking a break (to no doubt help his wife with all that diaper duty).
"I apologize to my fans and hope to be back in Madrid next year," he tweeted. "I'll be training near my home, and am excited to rejoin the Tour soon."