what season is once upon time on
Season Four is the fourth season of ABC 's Once Upon a Time. It was announced on May 8, 2014. Filming began on July 9, 2014 and lasted until April 2, 2015. Season Four premiered on September 28, 2014 with  A Tale of Two Sisters , and ended with  Operation Mongoose Part 1  immediately followed by  Operation Mongoose Part 2  on May 10, 2015.