Walt Disney Animation Studios has unveiled plans for Frozen Fever, a short film debuting in the spring that will feature characters from the No. 1 animated movie of all time. Directed by Jennifer Lee and Chris Buck, the Frozen spinoff will feature Anna, Elsa, Kristoff and snowman Olaf along with a new original song by Robert Lopez and Kristen Anderson-Lopez, who wrote the Oscar-winning Frozen hit “Let It Go.” In Frozen Fever, it’s Anna’s birthday, and Elsa and Kristoff are determined to give her the best celebration ever. But Elsa’s icy powers might put more than just the party at risk. The announcement was made tonight during the ABC making-of special The Story of Frozen: Making An Animated Classic.