Lillian Lethbridge-Stewart

Lillian Lethbridge-Stewart (nee McDougal) was the grandmother of Alistair and James Lethbridge-Stewart, the wife of Alistair 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)

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)

Behind the Scenes
The story What's Past is Prologue implies that Archibald Hamish Lethbridge-Stewart is the biological father of Gordon. If true, this suggests that Archibald and Lillian may have had an affair that resulted in the conception of Gordon.