In this work we present the analysis of the observations of Comet P/2019 LD2 (ATLAS) with the 10-m Gran Telescopio Canarias (GTC), La Palma, Spain. P/2019 LD2 (ATLAS, hereafter LD2), was discovered early June 2019 as a faint asteroidal object and later reported as the first known Jupiter trojan asteroid to display cometary activity. A closer examination of successive images, covering a longer arc in its orbit, showed that it is a Jupiter Family Comet (JFC), temporaly trapped by Jupiter from the Centaur population. LD2’s orbit just beyond Jupiter and its activity are evocative of 29P/Schwassmann-Wachmann, an object considered as a prototypical “gateway” between the Centaurs and JFCs by Sarid et al. (2019). The study of LD2 can help to better understand the transition from Centaur to JFC. We present the observations of P/2019 LD2 (ATLAS) obtained on May 16 and 17, 2020 using the OSIRIS camera-spectrograph of the 10.4 m GTC with the aim of modeling the behavior of the dust in the coma and discussing the nature of the activity of this comet. Additionaly, the images provided information of the orbit of this body that we use to study its past, present and future evolution. Finally, we also obtained two visible spectra of P/2019 LD2 on May 17, 2020 with the aim of looking for signatures of the typical gas species observed in comets. The nucleus of LD2 corresponds to a km-size object with a conspicuous coma and tail with a longitude > 1. There is no evidence of CN, C2 or C3 emmision. Our models of the dust reveal a maximum of emmision on November 27, 2019 with a total dust mass loss of 9×108 kg since the start of the dust emission (170 days before the maximum). P/2019 LD2 is now an ephemeral co-orbital of Jupiter, following what looks like a short arc of a quasi-satellite cycle that started in 2017 and will end in 2028. It will experience a very close encounter with Jupiter at ∼10 Jovian radii on January 18, 2063. The origin of P/2019 LD2 is still an open question. The probability of this comet having been captured from interstellar space during the last 0.5 Myr is 0.50±0.03, 0.79±0.06 during the last 2 Myr and to 0.89±0.07 for 4 Myr, suggesting that P/2019 LD2 could be a captured interstellar comet.