Ellen DeGeneres shared the announcement on her Instagram account Tuesday.
She also talked about it on her show.
Some details on the plot, from the Disney/Pixar press release:
Director and Pixar veteran Andrew Stanton takes audiences back to the extraordinary underwater world created in the original film. "There is no Dory without Ellen," said Stanton. "She won the hearts of moviegoers all over the world—not to mention our team here at Pixar. One thing we couldn't stop thinking about was why she was all alone in the ocean on the day she met Marlin. In 'Finding Dory,' she will be reunited with her loved ones, learning a few things about the meaning of family along the way."
According to Stanton, "Finding Dory" takes place about a year after the first film, and features returning favorites Marlin, Nemo and the Tank Gang, among others. Set in part along the California coastline, the story also welcomes a host of new characters, including a few who will prove to be a very important part of Dory's life.