Letitia's mother Catherine was the sister of the Hon. Mary Stewart, also daughter of the 1st Viscount Mountjoy; Mary was the mother of George Forbes, whom Letitia married on 16 July 1736; he inherited the title on the death of the 3rd Earl in 1765, at which point Letitia became Countess of Granard.
The earl and countess had one son, George (1740-1780), who succeeded to the earldom on his father's death in 1769. After this, Letitia was known as Countess Dowager of Granard. She died at Brockley Court in Somerset.[2]
