The Coldplay frontman and a male singer named Kevin performed the late singer's former band Wham!'s 1986 hit "Last Christmas." Martin played an acoustic guitar and provided backup vocals.
The performance took place on Dec. 27, two days after Michael died at age 53, at a shelter run by the London-based charity Crisis. A video was posted on the group's Facebook page Thursday and went viral.
"A huge thank you to Coldplay's Chris Martin for dropping by our Crisis at Christmas centres and entertaining our guests!" the post read. "Here he is performing a wonderful tribute to George Michael with our very own King of Karaoke - #CrisisXmas guest Kevin!"