  V473 Lyr is a classical Cepheid which is unique in having substantial
amplitude variations with a period of approximately 3.3 years, thought to be
similar to the Blazhko variations in RR Lyrae stars. We obtained an {\it
XMM-Newton} observation of this star to followup a previous detection in
X-rays. Rather than the X-ray burst and rapid decline near maximum radius seen
in $\delta$ Cephei itself, the X-ray flux in V473 Lyr remained constant for a
third of the pulsation cycle covered by the observation. Thus the X-rays are
most probably not produced by the changes around the pulsation cycle. The X-ray
spectrum is soft (kT = 0.6 keV), with
  X-ray properties which are consistent with a young low mass companion.
Previously there was no evidence of a companion in radial velocities or in {\it
Gaia} and {\it Hipparcos} proper motions. While this rules out companions which
are very close or very distant, a binary companion at a separation between 30
and 300 AU is possible. This is an example of an X-ray observation revealing
evidence of a low mass companion, which is important in completing the mass
ratio statistics of binary Cepheids. Furthermore, the detection of a young
X-ray bright companion is a further indication that the Cepheid (primary) is a
Population I star, even though its pulsation behavior differs from other
classical Cepheids.
