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Our Sun is powered by the fusion of hydrogen into helium that proceeds in the solar core via the two distinct mechanisms: dominant proton-proton (pp) chain and sub-dominant Carbon-Nitrogen-Oxygen (CNO) cycle. Neutrinos are emitted in electron-flavour eigenstate along several distinct reactions of both cycles, each characterized by a specific energy spectrum and flux. These so-called solar neutrinos are the only direct probe about the energy production mechanism of the Sun and the stars in general. Borexino, a 280-ton liquid scintillator detector that was taking data from May 2007 to October 2021 at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, is the only experiment to perform a comprehensive spectroscopy of pp chain solar neutrinos and to prove the existence of the CNO cycle. This was made possible thanks to an unprecedented radio-purity and thermal stability of the detector. The seminar will focus on the recent improved measurement of the CNO solar neutrino interaction rate at Earth obtained with the complete Borexino Phase-III dataset, that allowed us to exclude the absence of the CNO signal with about 7σ C.L. We used the new CNO flux measurement together with the 8B flux stemming from the global analysis of all solar neutrino data to evaluate the abundance of C and N with respect to H in the Sun with solar neutrinos for the first time. The details of the analysis as well as implications for the Standard Solar Model will be discussed in detail.