Published: 2021-07-18 01:19:53 BdST
In a moment of confusion during the ceremony, US film director Spike Lee jumped the gun and let slip the biggest secret of the night.
The violent film, which features the heroine, having sex with a car, had split critics, with some praising its originality while others were put off by its frantic and messy approach.
Ducournau, 37, had previously impressed critics with "Raw".
The world's biggest film festival returned to the French Riviera after a 2020 hiatus due to the coronavirus pandemic in one of the more unpredictable contests in years.