  Time series of spectroscopic, speckle-interferometric, and optical
long-baseline-interferometric observations confirm that $\nu$ Gem is a
hierarchical triple system. It consists of an inner binary composed of two
B-type stars and an outer classical Be star. Several photospheric spectral
lines of the inner components were disentangled, revealing two stars with very
different rotational broadening ($\sim$260 and $\sim$140 kms$^{-1}$,
respectively), while the photospheric lines of the Be star remain undetected.
From the combined spectroscopic and astrometric orbital solution it is not
possible to unambiguously cross-identify the inner astrometric components with
the spectroscopic components. In the preferred solution based on modeling of
the disentangled line profiles, the inner binary is composed of two stars with
nearly identical masses of 3.3 M$_\odot$ and the more rapidly rotating star is
the fainter one. These two stars are in a marginally elliptical orbit ($e$ =
0.06) about each other with a period of 53.8 d. The third star also has a mass
of 3.3 M$_\odot$ and follows a more eccentric ($e$ = 0.24) orbit with a period
of 19.1 yr. The two orbits are co-directional and, at inclinations of
79$^{\circ}$ and 76$^{\circ}$ of the inner and the outer orbit, respectively,
about coplanar. No astrometric or spectroscopic evidence could be found that
the Be star itself is double. The system appears dynamically stable and not
subject to eccentric Lidov-Kozai oscillations. After disentangling, the spectra
of the components of the inner binary do not exhibit peculiarities that would
be indicative of past interactions. Motivations for a wide range of follow-up
studies are suggested.
