He joined the Royal Household in 1937 at the time of the coronation of King George VI and Queen Elizabeth and was a Groom-in-Waiting to the king, an Extra Equerry in 1940 private secretary to then Queen Elizabeth, when he was appointed as Treasurer to the Queen, which became Treasurer to the Queen Mother upon the death of George VI. He was again appointed Groom-in-Waiting, to Queen Elizabeth II, in 1952.[2]
As a senior member of the royal household, he was a leading guest at the 1947 wedding of Princess Elizabeth and Philip, Duke of Edinburgh.
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He was made CVO in 1946, advanced to KCVO in 1949, and to GCVO in 1953.[1]
Penn was chairman of the billbrokers King and Shaxson, Ltd; Steward of the Courts at Eton; and he was the best man at the marriage of Harold Macmillan to Lady Dorothy Cavendish in 1920.[1]
He died a day before he was due to retire from royal service.