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The highest redshift quasars provide direct probes of the evolution of supermassive black holes openParSMBHsclosePar and the intergalactic medium at the earliest cosmic times. The discovery of a 7.8E8 Msun SMBH at z=7.54 openParJ1342+0928closePar put the strongest constrains on the seed BH and BH accretion history openParBanados et al. 2018closePar. Very recently comma our team has found an even more extreme object comma J1007 at z=7.5. J1007 is 1.8 times more luminous than J1342+0928 and hosts a SMBH with mass 1.6Eelev9 Msun comma two times more massive than J1342+0928. The existence of J1007 posts the most significant challenge to our understanding of the formation of the earliest SMBHs. Here comma we propose deep XMM-Newton observations to characterize the accretion properties of J1007 and investigate its formation and growth mechanisms.