Mustardseed is Puck's younger brother. His parents are Titania and Oberon. In Once Upon a Crime, Puck gives him the throne to Faerie since it is generally agreed that Mustardseed would be a better king than Puck would. However, in the second epilogue, it is vaguely implied that Puck went on to take his rightful place on the throne of Faerie, therefore, again, implying that Mustardseed was a 'Regent King' of sorts.