  SN 2019yvr is the second Type Ib supernova (SN) with a possible direct
detection of its progenitor (system); however, the spectral energy distribution
(SED) of the pre-explosion source appears much cooler and overluminous than an
expected helium-star progenitor. Using Hubble Space Telescope (HST) images and
MUSE integral-field-unit (IFU) spectroscopy, we find the SN environment
contains three episodes of star formation; the low ejecta mass suggests the SN
progenitor is most likely from the oldest population, corresponding to an
initial mass of 10.4$^{+1.5}_{-1.3}$ $M_\odot$. The pre-explosion SED can be
reproduced by two components, one for the hot and compact SN progenitor and one
for a cool and inflated yellow hypergiant (YHG) companion that dominates the
brightness. Thus, SN 2019yvr could possibly be the first Type Ib/c SN for which
the progenitor's binary companion is directly detected on pre-explosion images.
Both the low progenitor mass and the YHG companion suggest significant binary
interaction during their evolution. Similar to SN 2014C, SN 2019yvr exhibits a
metamorphosis from Type Ib to Type IIn, showing signatures of interaction with
hydrogen-rich circumstellar material (CSM) at >150 days; our result supports
enhanced pre-SN mass loss as an important process for hydrogen-poor stars at
the low mass end of core-collapse SN progenitors.
