Abstract Trojan asteroids are small bodies orbiting around the L 4 or L 5 Lagrangian points of a Sun-planet system. Due to their peculiar orbits, they provide key constraints to the Solar System evolution models. Despite numerous dedicated observational efforts in the last decade, asteroid 2010 TK 7 has been the only known Earth Trojan thus far. Here we confirm that the recently discovered 2020 XL 5 is the second transient Earth Trojan known. To study its orbit, we used archival data from 2012 to 2019 and observed the object in 2021 from three ground-based observatories. Our study of its orbital stability shows that 2020 XL 5 will remain in L 4 for at least 4 000 years. With a photometric analysis we estimate its absolute magnitude to be $${H}_{r}=18.5{8}_{-0.15}^{+0.16}$$ H r = 18.5 8 − 0.15 + 0.16 , and color indices suggestive of a C-complex taxonomy. Assuming an albedo of 0.06 ± 0.03, we obtain a diameter of 1.18 ± 0.08 km, larger than the first known Earth Trojan asteroid.