The fourth season of the American ABC fantasy-drama series Once Upon a Time was announced on May 8, 2014. On May 13, 2014, it was revealed that like the previous season, this season would also be split into two parts, the first half airing during autumn 2014, and the second half during spring 2015 of the 2014–15 television season. It premiered on September 28, 2014, and concluded on May 10, 2015. On April 20, 2014, it was announced that former Once Upon a Time in Wonderland star Michael Socha would be a series regular as his character Will Scarlet / the Knave of Hearts.