We have obtained a low-resolution optical spectrum for one of the faintest cluster member candidates in Praesepe with the Optical System for Imaging and low Resolution Integrated Spectroscopy mounted on the 10.4 m Gran Telescopio de Canarias. We confirm spectroscopically the first L dwarf member in Praesepe, UGCS J084510.66+214817.1. We derived an optical spectral type of L0.3±0.4 and estimated its effective temperature to Teff = 2279 ± 371 K and a mass of 71.1 ± 23.0 MJup, according to state-of-the-art models, placing it at the hydrogen-burning boundary. We measured the equivalent width of the gravity-sensitive sodium doublet at 8182/8194 Å, which adds credit to the membership of this new L dwarf to Praesepe. We also derived a probability of ˜20.5 per cent that our candidate would be a field L0 dwarf. We conclude that this object is likely to be a true member of Praesepe, with evidence of being a binary system.