Seth Costello is a fictional character from British soap opera, Hollyoaks. Son to Heidi and Carl Costello, he has a transgender twin Jasmine, later known as Jason. Younger brother to Riley, and uncle to Bobby, Seth is one of the grandchildren of psychopathic serial killer, Silas Blisset. Seth's major plot points include struggling with body image and turning to steroids, discovering his father's affair with his brother's fiancé, and being emotionally blackmailed by Warren Fox.