About the size of a walnut, Christie's had estimated it would sell for $3 million to $5 million. The flawless diamond is flanked on both sides by smaller pear-shaped diamonds. It's designed by Manhattan jeweler David Webb.
The buyer at Wednesdays's auction was not immediately identified.
Christie's said the previous record for a 30-carat square cut diamond was $3.1 million.
Annenberg died in March at age 91. She was U.S. Chief of Protocol in the Reagan administration. Her husband, billionaire publisher Walter Annenberg, died in 2002.
Francois Curiel, chairman of Christie's Europe and international head of jewels, said in a statement that the precious stone combines the best of the Four C's.
"[The diamond has] top color, perfect clarity, ideal cut and excellent [carat] weight. And if you add to this the impeccable provenance of the Annenberg name, you have one of the finest gems to appear on the market for many years," Curiel said.