We present the results of a new LUCI/Large Binocular Telescope near-infrared (NIR) spectroscopic observation PSO J030947.49+271757.31 (hereafter J0309+27), highest redshift blazar known to date ( z ∼ 6.1). From CIV λ 1549 broad emission line, we found that J0309+27 is powered by 1.45 −0.85 +1.89 × 10 9 M ⊙ supermassive black hole (SMBH) with bolometric luminosity ∼8 46 erg s −1 and an Eddington...