Chris Hemsworth freaks out as The Project host drops massive Thor: Ragnarok spoiler on air

So much for a spoiler alert.

[But also ~SPOILER ALERT~ if you're reading this article and don't want to know things about Thor: Ragnarok.]

When Australian icon Chris Hemsworth and all-around good guy Mark Ruffalo appeared on The Project on Monday evening to promote their new film, Thor: Ragnarok, they expected the hosts to keep major plot points for the film under wraps.

But alas, the hosts did not.

"The gorgeous Cate Blanchett plays your sister, Chris," said TV critic Tommy Little live on air. "And for a lot of this movie, your sister... she's trying to kill you."

This was the wrong thing to say.

"You can't say 'sister'!" cried 34-year-old Chris, bashing his fists on the newsdesk. "You can't give that away! This is not live is it? Can we rewind the tapes?"

They could not.

Mark, 49, hastily tried to distract with some Pig Latin while Chris cracked a few jokes.

Die-hard comic fans wouldn't have been shocked at the admission, however, as there are clear connections between Thor and Cate's character Hela in the books.

Still, this isn't the first time Thor: Ragnarok spoilers have dropped during this press tour. During the film's LA premiere, Mark accidentally livestreamed a portion of the movie from his pocket.

Thor: Ragnarok is in Australian cinemas on October 26.