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The aim of the project is to find the stars nearest to the Sun and tocontribute to the completion of the stellar and substellar census of the solarneighbourhood. We identified a new late-M dwarf within 5 pc, looking for highproper motion sources in the 2MASS-WISE cross-match. We collected astrometricand photometric data available from public large-scale surveys. We complementedthis information with low-resolution optical and near-infrared spectroscopywith instrumentation on the ESO NTT to confirm the nature of our candidate. Wealso present a high-quality medium-resolution VLT/X-shooter spectrum coveringthe 400 to 2500 nm wavelength range. We classify this new neighbour as anM7.0$\pm$0.5 dwarf using spectral templates from the Sloan Digital Sky Surveyand spectral indices. Lithium absorption at 670.8 nm is not detected in theX-shooter spectrum, indicating that the M7 dwarf is older than 600 Myr and moremassive than 0.06 M$_{\odot}$. We also derive a trigonometric distance of 4.4pc, in agreement with the spectroscopic distance estimate, making2MASS\,J154043.42$-$510135.7 the nearest M7 dwarf to the Sun. Thistrigonometric distance is somewhat closer than the $\sim$6 pc distance reportedby the ALLWISE team, who independently identified this object recently. Thisdiscovery represents an increase of 25\% in the number of M7--M8 dwarfs alreadyknown at distances closer than 8\,pc from our Sun. We derive a density of$\rho$\,=\,1.9$\pm$0.9$\times$10$^{-3}$\,pc$^{-3}$ for M7 dwarfs in the 8 pcvolume, a value similar to those quoted in the literature. This new ultracooldwarf is among the 50 nearest systems to the Sun, demonstrating that ourcurrent knowledge of the stellar census within the 5 pc sample remainsincomplete. 2M1540 represents a unique opportunity to search for extrasolarplanets around ultracool dwarfs due to its proximity and brightness.

2MASS J154043.42-510135.7: a new addition to the 5 pc population