  We study frustrated double ionization in a strongly-driven heteronuclear
molecule HeH$^{+}$ and compare with H$_2$. We compute the probability
distribution of the sum of the final kinetic energies of the nuclei for
strongly-driven HeH$^{+}$. We find that this distribution has more than one
peak for strongly-driven HeH$^{+}$, a feature we do not find to be present for
strongly-driven H$_{2}$. Moreover, we compute the probability distribution of
the n quantum number of frustrated double ionization. We find that this
distribution has several peaks for strongly-driven HeH$^{+}$, while the
respective distribution has one main peak and a "shoulder" at lower n quantum
numbers for strongly-driven H$_{2}$. Surprisingly, we find this feature to be a
clear signature of the intertwined electron-nuclear motion.
