Twitter user Zak S discovered the controller for sale on online marketplace OfferUp, and claimed to have purchased it for just $35.
The Series S has long been rumoured as a lower-spec version of the Series X, just like how Microsoft did it with the One X and One S. With Sony opting for the same specs for their PS5 standard and digital editions, it's not sure at this time what impact a performance-inferior machine will have on upcoming titles.
Slightly larger than the current-gen Xbox One controller, this model looks almost identical to its predecessor but for a circular D-pad and the addition of a third button in the middle. The logo on this button appears to indicate this is a Share button of some kind. It's also identical to the controller revealed with the Series X.
The fact that this is a white controller, instead of the black we've seen through official channels for Series X, could also suggest that the Series S may have a different colour scheme to the Series X.
This leak comes at a bad time for Microsoft, who could well be gearing up for a major reveal this month. With rumours suggesting a release in the next few months, there's likely going to be a short turnaround between any official announcement and preorders opening up.
Either way, we're bound to officially find out soon.
Images courtesy Zak S.