Georgina Adam fingers Leon Black as a possible buyer of the Raphael drawing Head of a Muse in the Financial Times:

it went to a buyer on the telephone, thought to be the US money manager and art collector Leon Black, who was involved in a tense bidding battle with the Old Master dealer Jean-Luc Baroni, who was in the room.

Adam also points to the polarization in the Old Master market where the top lots carried the London sales and the middle ground was missing.

What A Pair (Financial Times)