Lascelles was born on 11 April 1887 in the village of Sutton Waldron in Dorset, England, the sixth and youngest child and only surviving son of Commander Frederick Canning Lascelles and Frederica Maria Liddell, and the grandson of Henry Lascelles, 4th Earl of Harewood.^[1][2] He was thus a cousin of Henry Lascelles, 6th Earl of Harewood, who married Mary, Princess Royal, sister of his employers, Edward VIII and George VI. His mother was the daughter of Sir Adolphus Liddell, son of Thomas Liddell, 1st Baron Ravensworth.^[3]

After attending Marlborough College, followed by Trinity College, Oxford, Lascelles served in France with the Bedfordshire Yeomanry during the First World War, where he rose to the rank of captain and was awarded the Military Cross,^[4] after which he became aide-de-camp to his brother-in-law Lord Lloyd, the Governor of Bombay from 1919 to 1920.

Lascelles then returned to Britain and was appointed Assistant Private Secretary to Edward, Prince of Wales, in 1920, serving in that role until resigning in despair in 1929, citing differences with the prince.^[5]

From 1931 to 1935, he was Secretary to the Governor General of Canada, Vere Ponsonby, 9th Earl of Bessborough.

Lascelles then became the Assistant Private Secretary to George V in the latter months of 1935.^[6] When the Prince of Wales ascended the throne as Edward VIII on the death of George V in January 1936, Lascelles served briefly as the new King's Assistant Private Secretary, although he never saw the King during this phase.^{[5] [7]}

When Edward VIII abdicated in December 1936, Lascelles became Assistant Private Secretary to George VI, some time after the new king's accession.^[8]: So he did not resign again, but soldiered on through Edward's short reign and the protracted crisis of the abdication in 1936. He had been deeply shocked by the abdication, not dreaming until it was announced that it would happen, and the evening he heard of it he was so stunned that he went out and walked 3 times round St James Park in the darkness, thinking of James II .^[5]

In 1936 he became Assistant Private Secretary to King George VI.^[5]

Lascelles was knighted by George VI, while aboard a train, during the 1939 royal tour of Canada and the United States, which he had helped to arrange and manage; the King made him a Knight Commander of the Royal Victorian Order (KCVO)^[9] which is an honour in the personal gift of the sovereign and does not require political approval.^[10] He had been appointed a Companion of the Order of the Bath in 1937, was promoted to Knight Commander of the Order of the Bath in 1944 and to Knight Grand Cross on his retirement in 1953.^[9] He had been appointed a Member of the Royal Victorian Order in 1926, before his promotion to Knighthood in that Order in 1939.^[9] He was made a Companion of the Order of St Michael and St George in 1933.^[9] He was sworn of the Privy Council, entitling him to the prefix "Right Honourable", in 1943.^[9]

In 1943, Lascelles was promoted from Assistant Private Secretary to George VI to his Private Secretary, after effecting the forced resignation of Alec Hardinge, and served until the King's death in 1952. In 1952 he became Private Secretary to Elizabeth II, a role he held until the end of 1953, so overseeing the early days of her reign and the Coronation.^[5]

Lascelles was also Keeper of the Royal Archives from 1943 to 1953.^{[citation needed]}

He retired from his 27 years of royal service on the last day of 1953, at the age of 66.^[11] He had been asked by then Prime Minister Sir Winston Churchill twice and by the Queen once whether he would like to go to the House of Lords with a hereditary peerage but he declined.^[11] He did, however, accept appointment as a Knight Grand Cross of the Order of the Bath which, he said, "rated much higher than a peerage".^[11]

In 1955 Lascelles was very supportive of James Pope-Hennessy's commission to write an official biography of Queen Mary, although initially he wondered why and by whom this unknown young writer had been commissioned. Lascelles was a crucial witness for many key events, e.g. the abdication of Edward VIII. When the book passed the royal censors, Lascelles was livid that Pope-Hennessy phoned him with the news rather than coming round with the good news in person. ^[12]

Lascelles's papers are now held in the Churchill Archives Centre at Churchill College, Cambridge.^[13]

On 16 March 1920, Lascelles married Joan Frances Vere Thesiger (1895–1971), daughter of Frederic Thesiger, 1st Viscount Chelmsford, a former Viceroy of India and First Lord of the Admiralty.^[9]

They had three children:

• John Frederick Lascelles, born 11 June 1922, died 11 September 1951.
• Lavinia Joan Lascelles, born 27 June 1923, died 3 November 2020; married to Major Edward Westland Renton, divorced 1960, then 1962–64 to the writer Gavin Maxwell, and to David Hankinson in 1969.^[14]
• Caroline Mary Lascelles, born 15 February 1927; married 1949 to Antony Lyttelton, 2nd Viscount Chandos; then 1985 to David Erskine, son of Lord Erskine.

Lascelles died on 10 August 1981 at Kensington Palace at the age of 94.

• He also received the Royal Household Long and Faithful Service Medal.

Lascelles is portrayed by Paul Brooke in the 2002 film Bertie and Elizabeth and Pip Torrens in the 2016 Netflix series The Crown.

Lascelles, Rt. Hon. Sir Alan Frederick, (11 April 1887–10 Aug. 1981), Past Director: The Midland Bank; Royal Academy of Music; Private Secretary to the Queen, 1952–53; Keeper of the Queen’s Archives, 1952–53 (of the King’s Archives, 1943–52), doi.org/10.1093/ww/9780199540884.013.U166201 Who's Who

• The Papers of Sir Alan Lascelles at the Churchill Archives Centre