Cellian

 and his sister Ciara were known as the Irish Twins. He rarely spoke. While in nurse training, they stole pharmaceuticals, and were arrested. Doctor Ingrid Krafchin arranged for their release. The price was for their release was to be used as test subjects. She replaced their blood with Nestene Compound and incorporated Auton weaponry into his body, making them living weapons. Part of the process also gave them nanites which repaired any damage to them. (PROSE: Business Unusual)They were the pale man's most trusted employees, and infiltrated the Glasshouse for him. The Third Doctor stopped them and the pale man from using the technology in the Vault to take over the world. However, they all escaped being caught by UNIT. (PROSE: The Scales of Injustice)

encountered the Doctor again in 1989, in his sixth incarnation, along with Melanie Bush. By this time, though, they were having doubts about the work they were doing for the pale man. Melanie was captured and held by SeneNet, but escaped and was chased by the Stalker. The twins followed, but Cellian was attacked by the Stalker and lost his arm before Ciara could kill it. Her unemotional reaction to her brother's severe injury made Ciara realize how much of her humanity she had lost. After warning Mel about Krafchin, she took Cellian away. She hoped they could create a new life somewhere else, and make amends for all the wrongs they had committed. (PROSE: Business Unusual)

's arm grew back thanks to the nanites in him. By 1993, he and Ciara have settled in the village of Halcham and help out whenever they can. When the Cylox conflict reached the village, Ciara was fatally injured during the fighting. Due to their psychic connection, Cellian dies shortly thereafter. (PROSE: Instruments of Darkness)