Lillian Lethbridge-Stewart

Lillian Katherine Lethbridge-Stewart (née MacDougal (PROSE: The Ghosts of N-Space) or McDougal (PROSE: Island of Death) was the grandmother of Alistair and James Lethbridge-Stewart, the wife of Alistair Conall Hamish Lethbridge-Stewart, the mother of Gordon and Matthew Lethbridge-Stewart, and was the second cousin of Mario. (PROSE: The Ghosts of N-Space, Night of the Intelligence)

Biography
In her early life she was something of a socialite, and often travelled with a group of friends including a woman called Ruby. She met Alistair in May 1896 at the Palais Garnier, and it was 'love at first sight'. (PROSE: The Dinner Party, An Ordinary Man)

In 1902, while her husband was off on a mission, in a moment of loneliness she turned to her brother-in-law, Archibald Hamish Lethbridge-Stewart, and a night of indiscretion followed. Nine months later she gave birth to her second child, Gordon. Everyone believed the father to be Alistair. (PROSE: The Note)

The name 'Granny McDougal' stuck after James Lethbridge-Stewart learned about his grandmother's maiden name, and turned the song, "Old McDonald Had a Farm", into a song about her. (PROSE: Night of the Intelligence)

Circa 1925, she moved with her husband to the Stewart Estate in Appin, Scotland, where she became something of a socialite. In 1945, after receiving a telegram that Gordon was declared missing in action, Lillian went with her husband to Bledoe to attend a memorial service for her son. (PROSE: The Note)

According to a different account, she died when Alistair Gordon Lethbridge-Stewart was thirteen years old. (Although it's not stated if it was his maternal or paternal grandmother.) (PROSE: Island of Death)

The Brigadier told the Fifth Doctor that his grandmother died in 1955. (Although it's not stated if it was his maternal or paternal grandmother.) (PROSE: The King of Terror)

Alternative timeline
In a timeline created by the collapse of quantum nexus, Lillian never met Alistair in 1896, and instead happened upon Archibald in 1897 in Cromer, where the two fell in love and later married. As a result, Gordon was their only son and a very different life unfolded for all of them. (PROSE: An Ordinary Man)