Virginia Ogilvy, the Countess of Airlie, who served Queen Elizabeth II for nearly 50 years as the only American-born member of the monarch’s inner circle of advisers, assistants and close friends known as the ladies-in-waiting, died on Aug. 16 at her estate in Cortachy, a village in Scotland. She was 91.

Her daughter Lady Elizabeth Baring confirmed the death.

Ladies-in-waiting, a position dating to the Middle Ages, carried out different tasks under different queens, including planning, correspondence and household administration.

But in all cases the most important task was to serve as a sort of official best friend, requiring discretion, an ear for gossip and a careful eye on the queen’s needs and wants. By tradition and necessity, the role is usually held by a peer, in part because it comes without salary or benefits.

Lady Ogilvy’s husband, David, the Earl of Airlie, had been friends with Queen Elizabeth since they were children, and the couple were long a part of her social circle. Both would join her household: Lady Ogilvy in 1973 and her husband in 1984, taking the role of Lord Chamberlain of the Household, overseeing the queen’s domestic affairs after a long career in banking.

Lady Ogilvy was something of a first among equals in the ranks of the ladies-in-waiting, with the official title of Lady of the Bedchamber. She and the queen were by all accounts quite close; the queen even joined Lady Ogilvy at her 70th birthday party, at Annabel’s, a members-only nightclub in London, an event celebrated in the British news media as the only time the queen went clubbing.