Robert Downey Jr. just gave Marvel fans a heads up that another "big announcement" is planned for next week.

Marvel already surprised fans this month when they settled a deal with Sony Pictures to borrow Spider-Man for the Marvel Cinematic Universe. The next announcement is coming in eight days, according to Downey's Facebook page.

The "Iron Man" star posted a new poster of his character in "Avengers: Age of Ultron" along with this caption:

"Got a little something for ya, folks. Just cuz you're awesome, check out this new Iron Man poster for #Avengers #AgeOfUltron," he wrote on Feb. 25. "And don't tell 'em I told you, but there's a big announcement coming in 8 days... Shhhhhh... #getexcited."

Many speculate the announcement will have to do with Spider-Man again, but in what capacity is unclear.

Marvel has confirmed the web-slinging superhero will appear in an upcoming MCU movie, but most expect that to happen in "Captain America: Civil War" next year. The chances of him appearing in the new "Avengers" seems less likely since the movie wrapped filming before the Marvel-Sony deal came down.

Another idea, suggested by CinemaBlend, is that Marvel will announce the new Spider-Man actor. The studio has decided to recast the part after Andrew Garfield held the title in the last two "Amazing Spider-Man" movies. Possible casting includes another young Peter Parker or substituting in the "black Spider-Man," Miles Morales.

The first official "Avengers: Age of Ultron" movie poster recently confirmed the appearances of Anthony Mackie as Falcon and Hayley Atwell as Agent Carter. Composer Danny Elfman also showed up in the credits block for providing "additional music."

Elfman composed the score for Sam Raimi's first two "Spider-Man" movies as well as Ang Lee's "Hulk." The website io9 speculated this addition also could point to the inclusion of Spidey in the film.

Marvel still has one final trailer to release for the "Avengers 2" film. Early rumors had it premiering during the midseason premiere of "Agents of S.H.I.E.L.D." on March 3, but it's more likely to come later in March - perhaps two days later?

"Avengers: Age of Ultron" hits theaters on May 1.