Margaret Sheila Mackellar Chisholm (9 September 1895 – 13 October 1969) was an Australian socialite and "it girl" in British high society during and after World War I. She married three times: Francis St Clair-Erskine, Lord Loughborough (heir to the 5th Earl of Rosslyn); Sir John Charles Peniston Milbanke, 11th Bt; and Prince Dmitri Alexandrovich of Russia. Chisholm also had close relationships with brothers George VI and Edward VIII, both future Kings of the United Kingdom. Chisholm's romantic liaison with George ended when his father, George V, told him to leave the already-married Australian and find someone more suitable.
Known for her striking beauty, she is likely the inspiration for the Australian phrase "a good-looking sheila".
Sheila Chisholm was born on 9 September 1895 on the family property "Wollogorang", the centre of the locality now called Wollogorang, near Breadalbane, New South Wales, youngest child and only daughter of grazier Harry Chisholm and his wife Margaret (née Mackellar). Her paternal great-grandfather was Scottish and arrived in Australia with the Second Fleet in 1790. The Chisholms became wealthy members of the Squattocracy in New South Wales, and she was raised on "Wollogorang" with her two older brothers, John and Roy. As the only girl in a rough, male-dominated world, she often attempted to match and outdo the working men at tasks on the station. She recalled how she liked to "go out further than the furthest man" when swimming at Bondi Beach, until she witnessed a man lose his leg in a shark attack. Chisholm was also attracted to the arts and had a deep appreciation for Australia's flora and fauna. In her unpublished memoir, Waltzing Matilda, she described her adolescent self as "a queer mix of romanticism and boyishness ... I was quite unconscious of my looks".
Chisholm dated Italian-American actor Rudolph Valentino, who gifted to her his "lucky bracelet". He died six months later and Chisholm regretted it was because she had taken his luck. She is known to have inspired British author Evelyn Waugh to write his celebrated 1948 novel The Loved One.
Chisholm had fallen into obscurity by the time of her death and was almost completely forgotten until the publication of journalist Robert Wainwright's 2014 biography Sheila: The Australian Beauty Who Bewitched British Society.