The Monument to Alessandro di Sangro, situated in a niche to the left of the Altar, portrays the Patriarch of Alexandria and Archbishop of Benevento, son of the first Prince of Sansevero, Giovan Francesco di Sangro. The work is of dubious attribution. The decorative style recalls the environment and taste of Fanzago, and, on the basis of documentary evidence, Oderisio de Sangro, the family historian, has advanced the name of the sculptor Gian Domenico Monterosso of Vicenza.

The bust of Alessandro, shown in prayer and in Episcopal garb, appears stylised. The decoration is more successful, with its agile columns surmounted by compound capitals and two small angels resting on the architrave. The plaque, dictated in 1652 by his great-nephew Giovan Francesco di Sangro, fifth Prince of Sansevero, underlines the brilliant ecclesiastical career of his ancestor. Alessandro was the one who – as the inscription over the main entrance of the Sansevero Chapel states – rebuilt from the foundations and extended the “small chapel” his father had built, and had the first mass celebrated there in 1608, establishing the site as the final resting place of himself and his descendents.