The fourth season of the ABC fantasy-drama Once Upon a Time was announced on May 8, 2014. On May 13, 2014, it was revealed that the season would be split into two parts, the first half airing during fall 2014, and the second half during spring 2015 of the 2014–15 television season. It premiered on September 28, 2014.
On April 20, 2014, it was confirmed that former Once Upon a Time in Wonderland star Michael Socha would be a series regular as his character Will Scarlet/Knave of Hearts. The final minutes of the third season finale debuted Elsa. Kristoff and Anna from the 2013 Disney animated film Frozen have also since been introduced in Season 4 along with a new main antagonist, the Snow Queen, portrayed by Elizabeth Mitchell. The second half of the season will see the return of Kristin Bauer van Straten as Maleficent, in a recurring capacity for a "major arc.".