Now there's more!
Turns out the American Idol musician won't be the only one performing during the celebration...
Fellow season-10 Idol contestant Stefano Langone says he'll also be singing for the couple.
"I was in Salt Lake City and I played Nikki a song of mine, and she said, 'You need to play that at my wedding,' " Langone told us last night at Puma's Riddim and Run benefit event in Los Angeles.
"She absolutely loved it and I'm really excited to play for them," he said. "I love them both. They're great people and I can't wait to be there for them when they tie the knot."
Langone confirmed what McDonald previously teased, saying, "I know Paul will sing. He's that kind of guy."
One Idol season 10 star who may not be among the guests?
"Not yet!" Pia Toscano told us when we asked if she's received a wedding invite yet. "We'll see. As long as Paul's there and Nikki's there, that's all that you need."