Carl Holliday is the son of Jimmy King and Juliette Holliday who was conceived after a mix up at the fertility clinic which meant Juliette was impregnated with the wrong man's sperm. After the thought of looking after a child on her own got too much for her, Juliette left Carl with his father and he now lives with Jimmy, his wife Nicola - who Carl refers to as his mother and his half-siblings Elliot and Angelica.
Carl was conceived after a mix up at the fertility clinic meant Juliette was impregnated with Jimmy's sperm rather than that of her chosen donor. Juliette tracked down Jimmy so he could sign the papers that waved his rights to her unborn baby but she ended up going into labour at Jimmy's house, Mill Cottage. Jimmy's wife Nicola helped Juliette deliver a baby boy, whom she named Carl, unaware that it was also the name of Jimmy's deceased brother. Juliette initially allowed Jimmy to have access to Carl but that stopped when she and her estranged husband Greg reconciled and decided to be a proper family. Nicola guilt-tripped Juliette into allowing Jimmy to see baby Carl for one last time, but Nicola took him and ran away. Nicola returned not long afterwards and Juliette was persuaded not to press charges against her.
2016-: Return and raised by Jimmy and Nicola
In January 2016, Jimmy called Juliette to check up on Carl. Juliette appeared in the café and gave Carl to Jimmy explaining her husband had left her again. Jimmy agreed to look after Carl until Juliette had put her life back together. A few weeks later, Juliette agreed to give Jimmy parental responsibility as Carl was staying with Jimmy and Nicola on a more permanent basis.
After struggling to juggle childcare, Nicola became a stay-at-home mum to Carl, and his half-siblings Elliot and Angelica, but she soon became fed up and she and Jimmy switched roles so he became a full-time stay-at-home dad.
In January 2021, Juliette returned to the village, looking to get to know Carl now that she felt more able to care for him. Juliette's return was met with hostility from Jimmy and Nicola, who were understandably worried about losing Carl, and they insisted that Juliette leave them alone. However, the situation was taken out of their hands when Juliette approached Carl in the village, introduced herself as his Mother, and handed him a piece of paper with her mobile number on it. Carl told nobody expect Angelica about the note and, the following day, snuck out to meet Juliette. When Carl's absence was noticed, Jimmy and Nicola contacted the police and Angelica eventually revealed where Carl was. Juliette soon brought Carl home and told Jimmy and Nicola that, if they could not reach a compromise regarding access to Carl, she would not hesitate to involve solicitors. Whilst Jimmy refused to be threatened, Nicola was more sympathetic and, realising that Juliette had a genuine case, agreed to meet with her to discuss Carl. Jimmy was furious when he realised what Nicola had done, but soon came round when he realised that they couldn't keep Carl away from Juliette for good, especially now that the pair had met.
Juliette's return, along with Jimmy's involvement in the crash that claimed the life of Paul Ashdale, placed a huge strain on Jimmy and Nicola's marriage and Juliette managed to convince the pair that Carl should stay with her as a temporary measure. However, a short time later, Juliette announced that motherhood had not been what she expected and that she was going to follow her new boyfriend, Alistair, to New York, leaving Carl behind. By this point, Jimmy and Nicola had agreed to separate, with Jimmy staying elsewhere, but with Carl confused and upset by Juliette's departure, it was agreed that Jimmy should move back in.