  We studied the optical spectrum of HLX-1 during its latest outburst, using
the FORS2 spectrograph on the Very Large Telescope. We detect an Halpha
emission line centered at lambda = (6718.9 +/- 0.9) Ang and find that its
projected radial velocity with respect to the nucleus of ESO243-49 is (424 +/-
27) km/s, while the maximum rotational velocity of the stars in that galaxy is
~209 km/s. This suggests that HLX-1 and its surrounding stars were not formed
in situ, but came either from a disrupted dwarf galaxy or from a nuclear
recoil. We also find that the Halpha emission line is resolved with full width
at half maximum ~400 km/s, suggesting a nebular rather than disk origin for the
emission. Its luminosity (L_{Halpha} ~ a few 10^{37} erg/s, equivalent width
~70 Ang) is also consistent with emission from a nebula photo-ionized by HLX-1.
