Gunn: SYLVESTER STALLONE Plays a 'Very Important' Marvel Character in GUARDIANS OF THE GALAXY VOL.2

Also a previously top secret cast member is revealed.

via The Nerd Machine

http://www.newsarama.com/33634-gunn-sylvester-stallone-plays-a-very-important-marvel-character-in-guardians-of-the-galaxy-vol-2.html