After four years and two children together, Nicole Richie and Joel Madden are finally tying the knot the first weekend of December, according to X17online sources.

And now a source tells X17online exclusively that the couple are in talks with a very special wedding singer to perform during their big day!

A fellow club-goer at the Soho House in West Hollywood over the weekend (where Nicole, Joel and Christina Aguilera were all partying together) tells us:

    "Nicole and Christina were chatting non-stop about Nicole's upcoming nuptials. And I even overheard Nicole talking to Christina about possibly singing a song at Nicole's wedding!"

Christina normally commands about $1 million for a private performance, but somehow we think she won't charge for this one.

Not only did Christina attend Nicole's bachelorette party in Mexico in September, but a source tells us that Christina's been "practically living at Nicole's house" since her split from husband Jordan Bratman, where she's been spending a lot of time with a "certain guy." Like maybe Nicole's soon-to-be brother-in-law?