" 

 I would agree with  about not being sure that the sources given mention the subject; I would go further and suggest the sources need examination and verification here. As a priority, I would suggest that someone with JSTOR access examine the reference used for asserting that Patrick was the son of John O'Neill and a Madame de Buixin which is sourced to an article by Micheline Walsh, ""The Will of John O'Neill, Third Earl of Tyrone""; the article would of course be a reliable source, but we need to confirm that the details ascribed to this article are actually there. The Walsh article is available  here on JSTOR.  However there are other problems with the article  particularly with chronology that I can see: the article asserts that Patrick, born in 1622 and per the article, is the younger brother of Don Hugo Eugenio O'Neill. According to sources found for the article for Patrick's father, in particular  an article by Tomás Ó Fiaich (writing in his capacity as Professor of History at Maynooth rather than any clerical capacity), Don Hugo Eugenio was not born until after O'Neill seniors' 1630 trip to Madrid. While the article's assertion that ""he maintained a lengthy affair with a Countess of the O'Donnell family"" is true in the sense that Hugo's mother was Isabel O'Donnell and O'Neill senior and Isabel O'Donnell never married  and they were together long enough to produce Hugo and a sister Catalina,  all this happened during the 1630s  - not the 1620s  - and in Madrid, not in Brussels.  Another chronology problem raised by the O Fiaich  article is that it raises the prospect of a political marriage in 1627 between O'Neill senior and another O'Donnell, Mary Stuart O'Donnell. This marriage didn't happen, but we still have a problem; if O'Neill was married to Madame de Buixin in 1620 or 1621, what happened to her that left him free to marry in 1627 and yet have to make provisions for Madame de Buixin in his will in the late 1630s? · "