  The origin of the Lyman-${\alpha}$ (Ly${\alpha}$) emission in galaxies is a
long-standing issue: despite several processes known to originate this line
(e.g. AGN, star formation, cold accretion, shock heating), it is difficult to
discriminate among these phenomena based on observations. Recent studies have
suggested that the comparison of the ultraviolet (UV) and optical properties of
these sources could solve the riddle. For this reason, we investigate the
rest-frame UV and optical properties of A2895b, a strongly lensed
Ly${\alpha}$-emitter at redshift z ~ 3.7. From this study, we find that our
target is a compact (r ~ 1.2 pkpc) star-forming (star formation rate ~ 11
M$_{\odot}$/yr) galaxy having a young stellar population. Interestingly, we
measure a high ratio of the H${\beta}$ and the UV continuum monochromatic
luminosities (L(H${\beta}$)/L(UV) ~ 100). Based on tracks of theoretical
stellar models (Starburst99, BPASS), we can only partially explain this result
by assuming a recent (< 10 Myr), bursty episode of star-formation and
considering models characterised by binary stars, a top-heavy initial-mass
function (IMF) and sub-solar metallicities (Z < 0.01 Z$_{\odot}$). These
assumptions also explain the observed low (C/O) abundance of our target (~
0.23(C/O)$_{\odot}$). By comparing the UV and optical datasets, we find that
the Ly${\alpha}$ and UV continuum are more extended (x2) than the Balmer lines,
and that the peak of the Ly${\alpha}$ is offset (~ 0.6 pkpc). The
multi-wavelength results of our analysis suggest that the observed Ly${\alpha}$
emission originates from a recent star-formation burst, likely taking place in
an off-centre clump.
