  We present the first coordinated soft and hard 0.3-80 keV X-ray campaign of
the extragalactic supernova SN 2014C in the first $\sim$2307 d of its
evolution. SN 2014C initially appeared to be an ordinary type Ib explosion but
evolved into a strongly-interacting hydrogen-rich type IIn SN over $\sim1
\rm{yr}$. We observed signatures of interaction with a dense medium across the
X-ray spectrum, which revealed the presence of a $\sim 1-2 \rm{M}_{\odot}$
shell of material at $\sim6\times10^{16} \rm{cm}$ from the progenitor. This
finding challenges current understanding of hydrogen-poor core-collapse
progenitor evolution. Potential scenarios to interpret these observations
include (i) the ejection of the hydrogen envelope by the progenitor star in the
centuries prior to the explosion; (ii) interaction of the fast Wolf-Rayet (WR)
star wind with the slow, dense wind of the Red Super Giant (RSG) phase, with an
anomalously short WR phase.
