Co-creator Adam Horowitz confirmed the news on twitter ahead of the season 4 finale:
Season 5 of #OnceUponATime is officially a go! Thank you all for your support! Excited to bring you more!
— Adam Horowitz (@AdamHorowitzLA) May 8, 2015
The news comes after actor Josh Dallas who plays Prince Charming unwittingly revealed on US TV show KTLA that season 5 will begin filming in July.
Once Upon A Time airs on ABC in the US. UK fans can watch on Netflix.