The biopic -- which takes its title from Diana's maiden name -- unfolds over three days, as the royal family comes together to celebrate Christmas at the Queen's Sandringham Estate and Lady Di makes the decision to end her marriage with Prince Charles (Poldark's Jack Farthing).
The teaser, soundtracked with a cover of Lou Reed's "Perfect Day" sung by a children's choir, highlights the opulence surrounding Diana as she grapples with her unhappiness -- and seemingly does quite a bit of dancing. The final shot is of Diana and Maggie, the princess' dresser (played by Sally Hawkins), on the beach. "They know everything," Maggie says, to which Diana forebodingly responds, "They don't."
Hailing from director Pablo Larraín (Jackie) and Peaky Blinders creator Steven Knight, Spencer will premiere at the Venice Film Festival next month before screening at TIFF. "It's a really meditative project," Stewart told ET. "This is a really poetic, really internalized imagining of maybe the heaviest three days’ time before she does something as gnarly as leaving the royal family."