Junior was the name used by Jack Harkness for the son of the Empress of the Yalnix, whom he carried to term as an incubation chamber with the assistance of the midwife Jonty.
Due to Jack's recklessness, Junior used his psychic powers from his egg sac to turn the residents of Monkstone Abbey Health Spa. Jack, with Ianto Jones's help, delivered Junior in the birthing ship and handed him over to Jonty. Jonty told him that, once Junior came of age, he would take over from his mother as Ruler of the Yalnix. (AUDIO: Expectant)