Anne Catherine Tredick Mommand (née Wendell, previously known as the Countess of Carnarvon and Mrs Geoffrey Grenfell; November 25, 1900 – 1977) was an American heiress who married into the British aristocracy.

Catherine was born on November 25, 1900. She was the eldest daughter of Marian (née Fendall) Wendell (d. 1949)^[1] and Jacob Wendell III (d. 1911), of New York and Sandridgebury, Sandridge, Hertfordshire.^[2] Her younger sister, Philippa Fendall Wendell, was the wife of Randolph Stewart, 12th Earl of Galloway.^[3] Her brothers were Jacob Wendell (who married Eileen V. Carr) and Reginald L. Wendell.^[4][5]

Her father, a Harvard graduate and Broadway actor, died of pneumonia shortly before he was to appear in the leading role in What the Doctor Ordered at the Astor Theatre.^[6][7] Her maternal grandfather was Union soldier, Philip Richard Fendall III, and her great-grandparents were Elizabeth Mary (née Young) Fendall and Philip Richard Fendall II, the District Attorney of the District of Columbia. Her paternal grandfather was Jacob Wendell of Jacob Wendell Co.^[8]

On 17 July 1922, Catherine was married to Lord Porchester at St Margaret's, Westminster.^[9][4] He was the son and heir of George Herbert, 5th Earl of Carnarvon and Almina Herbert, Countess of Carnarvon and upon his father's death on 5 April 1923, Henry became the 6th Earl of Carnarvon and Catherine became Countess of Carnarvon.^[10] Before their divorce in 1936,^[11] they were the parents of two children:^[12]

• Henry George Reginald Molyneux Herbert, 7th Earl of Carnarvon (1924–2001), who married Jean Margaret Wallop, daughter of Hon. Oliver Malcolm Wallop, in 1956.^[13]
• Lady Anne Penelope Marian Herbert (1925–1990),^[5] who married her second cousin, Capt. Reinier Gerrit Anton van der Woude, son of R.A.G van der Woude and Mary Wendell (daughter of Harvard professor Barrett Wendell) in 1945.^[14]

After their divorce, Lady Carnarvon married, as his second wife, Lt.-Cdr. Geoffrey Seymour Grenfell (1898–1940) in 1938.^[15] Geoffrey was a son of Riversdale Francis John Grenfell (son of Charles Seymour Grenfell) and Cecil Blanche (née Lubbock) Grenfell.^[16] Grenfell died in action during World War II just two years after their marriage.^[17][18]

Ten years after his death, she married Don Stuart Momand (d. 1977) in 1950,^[19] who had previously been married to Virginia Ten Eyck Rice (a daughter of William Lowe Rice).^[20]

Catherine Mommand died in 1977.^[19]