We’ll try not to give away spoilers here but Mark Ruffalo kind of does that for us.
The actor appeared on Good Morning America with co-star Don Cheadle at Disney's D23 Expo in July 2017, during which he accidentally revealed the ending. However, he managed to turn it into a joke and no one copped that he’d accidentally let the truth slip.
You can see the mistake about 40 seconds in, and Cheadle’s reaction is genuinely gas:
— Good Morning America (@GMA) July 16, 2017
It wouldn’t be the first time Ruffalo has released one of Marvel’s critically guarded secrets – last year he accidentally live-streamed part of Thor: Ragnarok.