ArtNews identifies the seller as Adam Lindemann who bought the work in 2004 for $4.5m which might make the sale an even bigger coup than his Jeff Koons Hanging Heart sale in 2007. In that deal, Lindemann bought the work for $4m and sold it at Sotheby’s for $23.6m:

the painting figures prominently in the book David Adjaye: A House for an Art Collector, a luxe coffee table tome published by Rizzoli in 2011. It’s a celebration of the mansion at 77 East 77th Street that the British architect designed for Lindemann—Adjaye’s first private residence in New York—and combs carefully through the offerings in Lindemann’s collection. New York magazine has a slide show of eight images from the book on its website, and Untitled (Devil) appears in two of them.

A Basquiat From The Collection Of Adam Lindemann Could Break $48.8 M. Artist Record At Christie’s (ArtNews)