The 300th episode titles "Who Lives, Who Dies, Who Tells Your Story" focuses on victims of a rollercoaster accident.
The two victims remind the Grey Sloan doctors of George O’Malley (T.R. Knight) and Cristina Yang (Sandra Oh). (Watch the teaser below)
EW have also revealed that another patient will remind the doctors of Katherine Heigl's character Izzie Stevens and bring back memories of her.
With George, Cristina and Izzie (kind of) returning, it means there will be an original Fab Five interns reunion with Meredith Grey (Ellen Pompeo) and Alex Karev (Justin Chambers).
Showrunner Krista Vernoff revealed that the episode will be nostalgic love letter for fans.
"I have written it as a love letter to the fans who have been watching all 14 years," she said in an interview.
"If there is a feel to the episode, it is nostalgia. And if there is a theme of the episode, it is the ghosts of our past."