Collection of HSH Prince Nicolò and HSH Princess Rita Boncompagni Ludovisi, Rome.
One of the most valuable items to emerge from the new archival finds from the Villa Aurora is an autograph declaration in Latin and Italian dated 22 December 1552 by Ugo Boncompagni (1502-1585, from 1572 Pope Gregory XIII). Here Ugo confirms his paternity of Giacomo (or Jacopo) Boncompagni (1548-1612) by Maddalena de’ Fucchinis, a servant in the employ of his sister-in-law Laura Ferro.
The future Pope explains in detail the circumstances of the boy’s conception, which took place in 1547 in Bologna, after the Council of Trent had moved to that city; his motive was to assure his inheritance rights following the death (in 1546) of his father Cristoforo Boncompagni.
Collection of HSH Prince Nicolò and HSH Princess Rita Boncompagni Ludovisi, Rome.
Ugo, who had not yet taken holy orders, writes that he then arranged a dowry and marriage for Maddalena, with a mason Simone Scamni. The infant Giacomo was legitimated on 5 July 1548; by the mid-1570s he was one of the most powerful men in central Italy.
Collection of HSH Prince Nicolò and HSH Princess Rita Boncompagni Ludovisi, Rome.
In an accompanying note from 1870, the Boncompagni Ludovisi family archivist Enrico Narducci explains the chance find of what he terms this “precious document”; accompanying the manuscript is a modern transcription of the texts (apparently by later archivist Giuseppe Felici, in the 1940s).
This autograph declaration is not unknown: see e.g., the 1889 Lapi Italian edition of Michel de Montaigne (1533-1592), Journal du voyage en Italie (orig., 1774) 223 n. 1 (alluding to its “existence” and summarizing its contents).
Detail from portrait of Giacomo Boncompagni (1548-1612). Collection of HSH Prince Nicolò and HSH Princess Rita Boncompagni Ludovisi, Rome.
But no one has seen this document for at least 65 years—until now. (Full credit: it was Stéphanie Macarini Nadalo, FAAR’11, who first spotted it among the Boncompagni Ludovisi archival treasures.) The declaration sheds remarkable light on not just the fact of Giacomo’s descent from the future Pope Gregory XIII, but also precisely on the circumstances of his conception. And that makes this item unique, surely, in the annals of the Papacy.
Collection of HSH Prince Nicolò and HSH Princess Rita Boncompagni Ludovisi, Rome.
Portrait of Gregory XIII Boncompagni (1502-1572-1585) by Bolognese painter Lavinia Fontana (1552-1614)
Archivio Digitale Boncompagni Ludovisi 
[…] clear from an (unlabeled) illustration in the book that the ceiling fresco to the left shows the direct ancestor of the Princes of Piombino, Pope Gregory XIII (= Ugo Boncompagni, 1502-1572-1585), greeting the four […]