  We present a multi-instrument spectroscopic analysis of the unique Li/Na-rich
giant star 25664 in Omega Centauri using spectra acquired with FLAMES-GIRAFFE,
X-SHOOTER, UVES and HARPS. Li and Na abundances have been derived from the UVES
spectrum using transitions weakly sensitive to non-local thermodynamic
equilibrium and assumed isotopic ratio. This new analysis confirms the
surprising Li and Na abundances of this star (A(Li) =+2.71+-0.07 dex,
[Na/Fe]=+1.00+-0.05 dex). Additionally, we provide new pieces of evidence for
its chemical characterisation. The 12C/13C isotopic ratio (15+-2) shows that
this star has not yet undergone the extra-mixing episode usually associated
with the red giant branch bump. Therefore, we can rule out the scenario of
efficient deep extra-mixing during the red giant branch phase envisaged to
explain the high Li and Na abundances. Also, the star exhibits high abundances
of both C and N ([C/Fe]=+0.45+-0.16 dex and [N/Fe]=+0.99+-0.20 dex), not
compatible with the typical C-N anticorrelation observed in globular cluster
stars. We found evidence of a radial velocity variability in 25664, suggesting
that the star could be part of a binary system, likely having accreted material
from a more massive companion when the latter was evolving in the AGB phase.
Viable candidates for the donor star are AGB stars with 3-4 Msun and super-AGB
stars (~7-8 Msun), both able to produce Li- and Na-rich material.
Alternatively, the star could be formed from the pure ejecta of a super-AGB
stars, before the dilution with primordial gas occurs.
