Optical images (i band) of twoXXL clusters overplotted with X-ray contours (0.5–2.0 keV). Left panels: XLSSC 041 (in XXL-N), a C1 cluster at z = 0.142 with an estimated mass of M_500,MT ~ 8.3 × 10¹³M_⊙ and r_500,MT = 636 kpc. Right panels: XLSSC 561 (in XXL-S) a C2 cluster at z = 0.455 with an estimated mass of M_500,MT ~ 9.3 × 10¹³M_⊙ and r_500,MT = 993 kpc. The boxes indicate the position of AGNs with spectroscopic redshifts concordant with the respective cluster redshift. The bottom panels are zoomed-in images of the AGNs found in the black boxes. Both these AGNs are found in overdense regions, where galaxy interactions and merging are probable.