Mary Soames , Baroness Soames , ( née `` Spencer-Churchill '' ; 15 September 1922 -- 31 May 2014 ) was the youngest of the five children of Winston Churchill and his wife , Clementine .
Mary Soames , Baroness Soames LG DBE FRSL ( born Mary Spencer-Churchill ; 15 September 1922 -- 31 May 2014 ) was the youngest of the five children of the Prime Minister of the United Kingdom Winston Churchill and his wife Clementine .