  In light of the first observation of the semileptonic decay $B^{0}_{s}\to
K^{-}\mu^{+}\nu_{\mu}$ by the LHCb collaboration, we revisit the determination
of the CKM parameter $|V_{ub}|$ from exclusive semileptonic $B$-meson decays. A
controlled theoretical input on the Standard Model $B\to\pi$ and $B_{s}\to K$
vector and scalar form factors from Lattice QCD in the large $q^{2}$ region, in
combination with experimental measurements of the differential
$B\to\pi\ell\nu_{\ell}$ and $B^{0}_{s}\to K^{-}\mu^{+}\nu_{\mu}$ branching
ratio distributions, has allowed us determine $|V_{ub}|=3.86(11)\times10^{-3}$
and $|V_{ub}|=3.58(9)\times10^{-3}$ from the analyses of the individual decay
channels, respectively, and $|V_{ub}|=3.68(5)\times10^{-3}$ from a simultaneous
analysis of both decays, which is only a $1.4\%$ error and differs by
$1.8\sigma$ with respect to the value from inclusive determinations
$|V_{ub}|=4.25(12)^{+15}_{-14}(23)\times10^{-3}$. Our results are based on the
use of Pad\'{e} approximants to the participating form factors, highlight the
importance of the decay $B_{s}\to K\mu\nu_{\mu}$ in complementing the
traditional $B\to\pi\ell\nu_{\ell}$ one in the exclusive determination of
$|V_{ub}|$, and allow obtain, to the best of our knowledge, the first
correlated results for the $B\to\pi$ and $B_{s}\to K$ vector and scalar form
factors. We hope that our study strengthens the case for precise measurements
of the differential $B_{s}\to K\ell\nu_{\ell}$ decay rate with a finer
resolution of the $q^{2}$ bins, as it would definitely allow achieving more
conclusive results for $|V_{ub}|$.
