Zoom-in to the 10″ × 10″ region centred on the afterglow. Top: deep FORS2 I_Bessel-band image obtained 87 d after the GRB trigger. The red point indicates the ALMA localisation of the afterglow. A faint source, highlighted with a black circle, lies NW of the afterglow position. The radius of the circle is that of the aperture used for photometry. Bottom: for comparison, the HST/F140W image shows several sources at the position of the I_Bessel-band source. The cyan circle shows the location of the NIR afterglow and its error (Sect. 2.2), measured in the first HAWK-I H-band observation.