Madonna has offered to remarry ex-husband Sean Penn ... for $150k.

While it sounds like something of an indecent proposal, it was in fact all for a charitable cause, as the pop star staged 'an evening of music, art and mischief' in aid of her charity Raising Malawi.

The Material Girl and Penn tied the knot in 1985 and were married for four years before Madonna filed for divorce. But the 58-year-old, who later married British film director Guy Ritchie, has often described Penn as the "love of her life."

And as he attended the high-profile event she couldn't miss the opportunity to profess her love for her ex-husband once more, announcing in front of an audience of A-lister stars: "I'm still in love with you.'

Taking to the stage at Miami's Art Basel on Friday (2 December) night, the singer auctioned off items of jewellery and works of art from her personal collections.

Honing in on her ex, she made the unusual marriage proposal as she persuaded the Oscar-winner to bid for her jewels. While Penn took her up on the offer, he lost out to another wealthy buyer who outbid him for the jewellery.

However it didn't stop the pair taking a trip down memory lane that was fueled with sexual innuendo. Joining his ex-wife on stage, the Milk actor crawled under her legs as she flirtatiously asked him if it reminded him of anything.

Sean then handcuffed Madonna as the singer joked: "The many moments that were our marriage."

It was however apt for the pair to reunite, at least on stage, as they auctioned off a series of intimate unseen photographs from their 1985 wedding taken by celebrity photographer Herb Ritts.

Keeping her promise to offer an evening of mischief to her celebrity guests that included Leonardo DiCaprio, Madonna put on a burlesque performance and performed a musical number with Arianna Grande.

She also paid tribute to Britney Spears, performing her own rendition of the singer's 2003 hit song Toxic that sent Twitter into raptures.

With British funny man James Cordon as the master of ceremonies, the Rebel Heart singer also enlisted the help of some of celebrity friends, with Chris Rock, David Chappelle and David Blaine auctioning items, while others offered to share some unique experiences in exchange for donations to the charity, Mail Online reports.

Actors Edward Norton and Jonah Hill offered a private game of poker; magician Blaine would give a private performance to the highest bidder while one lucky person had the chance to spend a week at DiCaprio's Palm Spring house.

And it was all worthwhile, as the VIP event raised substantial funds which will go towards building a pediatric surgery and intensive care unit in Malawi.

Madonna – whose son David Banda and daughter Mercy, 10, are from Malawi - started Raising Malawi in 2006.