The pair attended Sean Penn's fundraiser for Haiti relief, and Martin was the winning bidder for a painting by famed graffiti artist, Banksy.
Called Heart Balloon, the painting is of - well, a ballon - and Gwynie couldn't stop smiling and laughing as her Coldplay husband outbid the competition for the artwork.
But even at $650,000, Martin wasn't the biggest bidder at the Help Haiti Home gala.
Koons will be making that unique piece of art out of 24 firearms Penn decided to get rid of at the suggestion, he revealed, of a "strong-willed woman from South Africa" who wanted them out of his house. That would be Penn's new girlfriend, Charlize Theron .