Gordon was born in late September 1990. He was brought up by Kate as a single parent, initially aboard a narrow houseboat moored on an English canal. His father, Jonathan, chose not to be a part of his and his mother's lives after Kate refused to marry him. (PROSE: Downtime)
Gordon was nearly five years old before he met his grandfather, Alistair, Kate having kept her pregnancy and Gordon's existence a secret from her father. Following recent events at New World University, Gordon acquired an imaginary friend called Danny and mentioned this on first meeting his grandfather. (HOMEVID: Downtime)
Behind the scenes
The in-universe article A Brief History of the Lethbridge-Stewarts, available as a download from the Lethbridge-Stewart website, says Gordon Lethbridge Stewart III "is making waves of his own". Because it is non-narrative, it is not a valid source on this wiki.