This study deals with the New Cathedral of Lérida —Catedral Nova de Lleida, in Catalan— disappeared main altarpiece, a masterpiece of Aragonese sculptor Juan Adán (1741-1816); and it intends to complete the 1780 project history. Just before his termination, this work was destroyed in the tragic July 1782 fire, for which this Aragonese sculptor was accused. Thanks to different archives exhaustive analysis, it can be determined his circumstances —evidence, persons involved, consequences— without which the sense of history and missing heritage would be incomprehensible. Hence, this study unites numerous dispersed materials, with the previously unknown documents concerning this tragic event addition and this Juan Adán’s work real scope.