Pop superstar Madonna gave fans a special treat at a secret gig on Wednesday - by bringing Justin Timberlake onstage to sing with her.

The Material Girl was performing for a select group of fans at New York's Roseland Ballroom to celebrate the U.s. release of new album Hard Candy when her surprise guest was revealed.

During the 40-minute set - the first time Madonna had performed tracks from Hard Candy live - she was joined by Timberlake for a performance of single 4 Minutes, which they had collaborated on.

After thanking Timberlake for joining her, Madonna told the crowd she felt "like the luckiest girl in the world to be able to make a record with him, Timbaland, Pharrell (Williams), Kanye West.

"And even though I've made what seems like 100 records, every time I put one out it's like the first time, and the best time."

And the kind-hearted star rewarded fans who didn't manage to obtain tickets for the free show by streaming the performance online, reports GigWise.com.