  We present X-ray and optical observations of nova V407 Lup (Nova Lup 2016),
previously well monitored in outburst, as it returned to quiescent accretion.
The X-ray light curve in 2020 February revealed a clear flux modulation with a
stable period of 564.64$\pm$0.64 s, corresponding to the period measured in
outburst and attributed to the spin of a magnetized white dwarf in an
intermediate polar (IP) system. This detection in quiescence is consistent with
the IP classification proposed after the nova eruption. The XMM-Newton EPIC
X-ray flux is about 1.3 $\times 10^{-12}$ erg/cm$^2$/s at a distance, most
likely, larger than 5 kpc, emitted in the whole 0.2-12 keV range without a
significant cut-off energy. The X-ray spectra are complex; they can be fitted
including a power law component with a relatively flat slope (a power law index
of about 1), although, alternatively, a hard thermal component at kT$\geq$19
keV also yields a good fit. The SALT optical spectra obtained in 2019 March and
2022 May are quite typical of IPs, with strong emission lines, including some
due to a high ionization potential, like He II at 4685.7 Angstrom. Nebular
lines of O [III] were prominent in 2019 March, but their intensity and
equivalent width appeared to be decreasing during that month, and they were no
longer detectable in 2022, indicating that the nova ejecta dispersed. Complex
profiles of the He II lines of V407 Lup are also characteristic of IPs, giving
further evidence for this classification.
