Britain’s Prince Charles celebrated his 65th birthday at Buckingham Palace with a host of American guests — telling them of his joy of becoming a grandfather to Prince George. The Prince of Wales’s birthday dinner was hosted by London power couple Cyrus and Priya Vandrevala, international venture capitalists who moved to the British capital five years ago. Guests included Metro-Goldwyn-Mayer CEO Gary Barber, US society doyennes Mercedes Bass and Lynn Wyatt, Judith Giuliani along with two couples from Philadelphia, software entrepreneur Michael Sanchez and publicist wife Nancy Assuncao and Walt and Sue Buckley of Internet Capital Group. Charles mingled with guests over cocktails and discussed the importance of philanthropy, and a source said he described “how he really enjoyed being a grandfather and how he wished he had grandchildren earlier. He said he was envious of his friends who already have many grandchildren.” Also there were Charles’ wife, Camilla Parker-Bowles, and Winston Churchill’s grandson Nicholas Soames. We’re told Charles told his guests from Philadelphia how he liked the city and that he met with the late philanthropist Leonore Annenberg during a 2007 visit and was impressed with how she supported the arts. He added, “The Americans really get it right with how philanthropic they are.”