Multi-wavelength images of J0217−0820. Left to right: RGB images from the DESI Legacy Imaging Surveys; ALMA images at 870 μm, 1.2 mm, 1.5 mm, and 2.0 mm. In the ALMA images, the central blazar has been removed; The orange ellipse shows the FWHM of the synthesized beam and the white contours show the emission 3σ above the rms noise. Except for the blazar, all the other sources are invisible in the optical image.