Rumoured to be unlocked by obtaining all the trophies in The Sly Collection, the supposed trailer was captured by Youtube user 'tatermoog.' It shows Sly's silhouette peeking out at a patrolling guard and ends with a logo for 'Sly 4,' subtitled simply with a question mark.
Sly creator Sucker Punch has yet to announce a fourth game in the series, nor its next project after inFamous 2, which hits PlayStation 3 in 2011.
Shacknews has contacted Sucker Punch and long-time publishing partner Sony for comment. For now, watch the trailer below but do take it with a pinch of salt.