The KM3NeT ultra-high-energy event

A neutrino event of exceptional energy, in the hundreds of PeV regime, was detected with the KM3NeT-ARCA detector. At the time of the detection, on February 13, 2023, the ARCA detector consisted of 21 detection lines, about 10% of the total volume of the full planned detector. This ultra-high-energy event lies in an unexplored energy range where cosmic neutrinos have been predicted but never observed until now. The KM3NeT Collaboration has considered several hypotheses regarding the possible origin of this event, though no clear indication has been found yet. In this contribution, the details of the event energy and direction reconstruction, together with the investigated hypotheses on its nature, will be reported.