  The supernova remnant (SNR) candidate G 116.6-26.1 is one of the few high
Galactic latitude ($|b| > 15^o$) remnants detected so far in several wavebands.
It was discovered recently in the SRG/eROSITA all-sky X-ray survey and displays
also a low-frequency weak radio signature. In this study, we report the first
optical detection of G 116.6-26.1 through deep, wide-field and higher
resolution narrowband imaging in $\rm H\alpha$, [S II] and [O III] light. The
object exhibits two major and distinct filamentary emission structures in a
partial shell-like formation. The optical filaments are found in excellent
positional match with available X-ray, radio and UV maps, can be traced over a
relatively long angular distance (38' and 70') and appear unaffected by any
strong interactions with the ambient interstellar medium. We also present a
flux-calibrated, optical emission spectrum from a single location, with Balmer
and several forbidden lines detected, indicative of emission from shock
excitation in a typical evolved SNR. Confirmation of the most likely SNR nature
of G 116.6-26.1 is provided from the observed value of the line ratio $\rm [S\,
II] / H\alpha = 0.56 \pm 0.06$, which exceeds the widely accepted threshold
0.4, and is further strengthened by the positive outcome of several diagnostic
tests for shock emission. Our results indicate an approximate shock velocity
range $70-100\, km\, s^{-1}$ at the spectroscopically examined filament, which,
when combined with the low emissivity in $\rm H\alpha$ and other emission
lines, suggest that G 116.6-26.1 is a SNR at a mature evolutionary stage.
