  The recent detection in archival HST images of an object at the the location
of supernova (SN) iPTF13bvn may represent the first direct evidence of the
progenitor of a Type Ib SN. The object's photometry was found to be compatible
with a Wolf-Rayet pre-SN star mass of ~11 Msun. However, based on
hydrodynamical models we show that the progenitor had a pre-SN mass of ~3.5
Msun and that it could not be larger than ~8 Msun. We propose an interacting
binary system as the SN progenitor and perform evolutionary calculations that
are able to self-consistently explain the light-curve shape, the absence of
hydrogen, and the pre-SN photometry. We further discuss the range of allowed
binary systems and predict that the remaining companion is a luminous O-type
star of significantly lower flux in the optical than the pre-SN object. A
future detection of such star may be possible and would provide the first
robust identification of a progenitor system for a Type Ib SN.
