  The morphology and optical spectrum of IPHASXJ210205+471015, a nebula
classified as a possible planetary nebula, are however strikingly similar to
those of ATCnc, a classical nova shell around a dwarf nova. To investigate its
true nature, we have obtained high-resolution narrow-band [O III] and [N II]
images and deep GTC OSIRIS optical spectra. The nebula shows an arc of [N
II]-bright knots notably enriched in nitrogen, whilst an [O III]-bright
bow-shock is progressing throughout the ISM. Diagnostic line ratios indicate
that shocks are associated with the arc and bow-shock. The central star of this
nebula has been identified by its photometric variability. Time-resolved
photometric and spectroscopic data of this source reveal a period of 4.26
hours, which is attributed to a binary system. The optical spectrum is notably
similar to that of RWSex, a cataclysmic variable star (CV) of the UXUMa
nova-like (NL) type. Based on these results, we propose that IPHASX
J210205+471015 is a classical nova shell observed around a CV-NL system in
quiescence.
