The existence of supermassive black holes (SMBHs) powering luminous quasars at z∼6 and beyond, presents a severe challenge for extragalactic astronomy. The theory argues that these objects must have formed and grown within the most massive dark matter halos in highly biased regions of the early Universe, where seed black holes may find suitable physical conditions to form and sufficiently large reservoirs of gas to grow. Such early large-scale structures are expected to be traced by significant galaxy overdensities that may extend up to ∼10 physical Mpc from the central quasar. I will present the spectroscopic confirmation of a large-scale structure around the z=6.31 QSO SDSS J1030+0524, powered by a one billion solar mass black hole. The structure is populated by at least six galaxies, and our is the first spectroscopic identification of a galaxy overdensity around a supermassive black hole in the first billion years of the Universe. This important discovery is the result of a long-time work conducted by a group of researchers, mainly from INAF and in particular from OAS in Bologna. The first observations, obtained with the prime focus camera LBC mounted on the Large Binocular Telescope, date back to more than eight years ago and, meanwhile, we collected both proprietary and archived observations toward the field around QSO J1030+0524, which make it one of the most studied region of the sky across the entire electromagnetic spectrum: an INAF legacy field. (Visit the web site http://j1030-field.oas.inaf.it/)