 The painting is one of only a few by Raphael to remain in private hands |
The portrait, of Florentine ruler Lorenzo de' Medici, had not been seen in public since 1968.
When it was last sold, the art world was divided over its origins and it sold for just $325.
But experts now agree it is genuine - Christie's auctioneers describing it as the most important Renaissance portrait to be sold at auction for a generation.
'Blind date'
The portrait was commissioned by Pope Leo X after he arranged a marriage between his nephew, Lorenzo de' Medici, and Madeleine de la Tour d'Auvergne, a cousin of Francois I, King of France.
The couple had never met, and so Raphael's paintings were to serve as an introduction - in a Renaissance version of the blind date.
In his portrait, Lorenzo is seen dressed in a gold tunic and fur-lined cape, resplendent against a rich green background.
The Pope's introduction seems to have worked - the couple married in 1518 and had a daughter, Catherine de' Medici, who went on to marry King Henry II of France.
Record broken
Raphael started out as a competent master of provincial church decoration and became one of the greatest painters of his era.
The sale has broken the record for a price paid for a work by Raphael.
The previous highest price was £5.3m in 1996 for Study for the Head and Hand of an Apostle, a drawing in black crayon.
Richard Knight, international director of Christie's Old Master Department, said: "The importance of the artist and the sitter, together with the provenance and the historical context behind this painting's creation, make it one of the most significant old master pictures to be offered at auction for a generation."