Jonathan James
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A man called Jonathan had sex with Kate Stewart and they had a son, Gordon Lethbridge-Stewart. Kate didn't wanted Gordon to loose the family name, Lethbridge-Stewart, so Jonathan and Kate never married, even though Jonathan wanted so. When Gordon was two they split up. (PROSE: Downtime) Gordon never saw his father again, (HOMEVID: Downtime) nor did Kate. (TV: Death in Heaven)