  We report the successful synthesis of a new 4$d$ based polycrystalline
inverse Heusler alloy Fe$_2$RuGe by an arc melting process and have studied in
detail its structural, magnetic and transport properties complemented with
first principle calculations. X-ray and neutron diffraction, Extended X-ray
Absorption Fine Structure and $^{57}$Fe M\"{o}ssbauer spectroscopic studies
confirm the single phase nature of the system where the Fe and Ru atoms are
randomly distributed in the 4$c$ and 4$d$ Wyckoff positions in a ratio close to
50:50. The formation of the disordered structure is also confirmed by the
theoretical energy minimization calculation. Despite the random cross-site
disorder of Fe and Ru atoms, magnetic measurements suggest not only a high
Curie temperature of $\sim$860\,K, but also a large saturation magnetic moment
$\sim$4.9\,$\mu_B$ per formula unit at 5\,K, considerably exceeding the
theoretical limit (4\,$\mu_B$ per formula unit) predicted by the Slater-Pauling
rule. Only a few Fe-based inverse Heusler alloys are known to exhibit such high
Curie temperatures. Neutron diffraction analysis coupled with the isothermal
magnetization value indicates that the magnetic moments in Fe$_2$RuGe are
associated with Fe-atoms only, which is also confirmed by M\"ossbauer
spectrometry. Interestingly, in comparison to the cubic or hexagonal phase of
the parent compound, Fe$_3$Ge, the Curie temperature of Fe$_2$RuGe has
increased significantly despite the substitution of the nonmagnetic, yet
isoelectronic element Ru in this structurally disordered compound. Our
theoretical calculation reveals that the large Fe moment ($\sim2.8\mu_B$/Fe) on
the 4$b$ site can be attributed to a charge transfer from this Fe site towards
its Ru neighbours. Such a substantial increase in magnetic moment due to
electron charge transfer has not previously been reported in a Heusler alloy
system.
