He's selling the drawing through Sotheby's, with all proceeds going to Panthera, his wild cat conservation charity.

A rare Rembrandt drawing, Young Lion Resting, could fetch up to $20 million at auction, with proceeds supporting wild cat ...

Picture a darkly-lit hall, its plum-colored walls lined with dozens of paintings, all masterpieces from the Dutch Golden Age — Rembrandt, Hals, even a Vermeer, almost all framed in thick, black wood.