A younger incarnation of Dorothy has already appeared on the show, played by Matreya Scarrwener in a season 3 episode, reported Entertainment Weekly.
"Once Upon A Time" is currently on a winter break but will be returning in the new year ready for its 100th episode.
Many characters will make their reappearance for the event, including Sidney Glass (Giancarlo Esposito), Peter Pan (Robbie Kay) and Cora, the Queen of Hearts (Barbara Hershey).
Also returning - but not for the 100th episode - is Cruella de Vil (Victoria Smurfit) while the show will also introduce Jonathan Whitesell and Kacey Rohl as Hercules and Meg.