She was her grandmother's favourite grandchild and closest confidante.
The highly influential Duchess of Marlborough tried to arrange a secret marriage between Lady Diana and the Prince of Wales, King George II's eldest son and heir apparent to the throne.
When the scheme was frustrated by Prime Minister Robert Walpole, Lady Diana was married off to Lord John Russell, later 4th Duke of Bedford.
The couple's only child was a son named John, whose preterm birth was induced by a carriage accident and who lived for a day.
Following a further miscarriage, the Duchess of Bedford died of tuberculosis at the age of 25.
Her brother John's descendant Lady Diana Spencer, who married Charles, Prince of Wales, in 1981, was named after her.