SAN DIEGO - I think it's pretty certain at this point that the much-ballyhooed "Hulkbuster" fight in "Avengers: Age of Ultron" is gonna be a feast for the eyes - but will it be a feast for the heart too? Robert Downey Jr. thinks so.

"It can't just be a good fight, it's gotta be about something," said Downey Jr. while promoting the upcoming sequel at San Diego Comic-Con. "And the great thing in 'Age of Ultron' is, that fight between [the Hulk and Tony Stark] is, nobody wins when two people who are friends fight."

Speaking of friends (or at least former colleagues) Downey Jr. had a chance to reunite with his "Less Than Zero" co-star James Spader on the film, and - echoing the sentiments of their mutual co-star Chris Hemsworth - the actor told us to expect real fireworks when the "Blacklist" star hits the screen as the titular baddie.

"The Marvel universe has never seen anything what like Jimmy Spader is doing," said Downey Jr. "If this footage is any indication, just get ready. Strap in!"

To hear more from Downey - including even more talk about the Hulkbuster brawl and praise for first-time "Avengers" stars Aaron Taylor-Johnson, Elizabeth Olsen and Paul Bettany - click on the video above for the full interview.

"Avengers: Age of Ultron" hits theaters on May 1, 2015.