Frances Helen Sweeny was born on 19 June 1937 at Beaumont House, a nursing home in
Marylebone Lane,
London, to American amateur golfer, socialite and businessman
Charles Francis Sweeny and his wife, Scottish debutante
Margaret Whigham. Her mother had suffered eight miscarriages and given birth to a stillborn daughter prior to her birth. She was baptised in the
Catholic Church on 21 July 1937 at the
Brompton Oratory. She had one younger brother, Brian Charles Sweeny (1940–2021). Her parents divorced in 1947. Her mother subsequently married the
11th Duke of Argyll in 1951 and scandalously divorced him in 1963. Frances and her brother were largely raised by their mother's cook. She attended
finishing school in Florence and Paris and was acclaimed "
debutante of the year" in 1955. ==Marriage and family==