Until now there has been no confirmation if the last instalment of Stephenie Meyer's best-selling book series would be filmed.
It is thought the 754-page novel might be split into two feature films along the same lines as Harry Potter and the Deathly Hallows, with hopes New Moon director Chris Weitz will return to the helm.
While Serratos's Eclipse co-stars Gil Birmingham, Daniel Cudmore and Booboo Stewart remained coy about the film's start date, the actor and sometime model accidentally let the cat out of the bag.
"No word is out yet," Booboo Stewart said, to which Serratos quickly replied "No, October."
Birmingham, who plays Taylor Lautner's father Jacob Black, quickly tried to cover up the blunder.
"We could tell you, but we'd have to kill you - like we will Christian," he said.
The four Eclipse stars, who flew out today, have been in Australia for the Twilight convention held at Melbourne University on Sunday.
Serratos said she had got used to the Twilight mania.
"People say it is like Beatle-mania," Serratos said.
"But after a while it becomes second nature, I mean it has nothing to do with you and everything to do with the character you're playing.HeraldSun via source
Don't you love slip-ups? There is too much truth in them. lol Gil Birmingham was too cute to "save" Christian's funny slip.