He had received identical training to that of the Gallifreyan Gat. Lee was rewarded with a medal made of chronotelluric alloy for his service. It was considered by Gat that Lee died at some point. According to her, they had "such a moving funeral for [him]".
In fact, he accompanied the Doctor while she hid on Earth in the early 21st century, in order to protect her while she became the unsuspecting human "Ruth Clayton" using a Chameleon Arch. He posed as her husband while they lived together in Gloucester, working at Bathrooms4U and claiming to be from Stroud and that his family is from somewhere near Gloucester. Some of his actions were not considered normal by Allan, who worked as a barista in a local cafe. According to him, Lee hardly talked to anyone, cut his own hair, got weird books from the library. Trying to investigate that, Allan made a dossier on Lee.
In 2020 the Judoon came to Earth looking for a fugitive. Lee became very nervous when he learned about that. He planed to escape Gloucester with "Ruth" but was informed by the Thirteenth Doctor that half of the city was isolated by the zonal enforcement field. Lee asked "Ruth" to wait for him inside the Gloucester Cathedral while he planned to face the Judoon. He was executed by Gat, who had been hired to track down the "Fugitive" Doctor. (TV: Fugitive of the Judoon)