Carl was the prince of Montmartre, which was north of Paris, France. He was a childhood friend of Clare Arnold. Their families were close and Carl and Clare always played together, with Carl usually getting into trouble and blaming Clare.
In season 6, Prince Carl showed up and boldly pursued Clare, who was already in a relationship with Steve Sanders. However, he and Steve got along really well, with Carl even throwing Steve a huge birthday party aboard the Queen Mary in Long Beach.
Clare was not interested in Carl, but knew it was her late mother's wish that she marry him. She was also annoyed at the seeming indifference of Steve, who stepped aside to let Carl have his chance. However, Carl was unsuccessful in his pursuit of Clare, who was deeply in love with Steve and chose her own path rather than follow her mother's wishes. Carl returned to his country shortly thereafter.