In 1689 Diarmaid MacLochlainn became the last person known to have exercised the chiefship of the clan by raising a company of soldiers at his own expense to fight against the forces of William of Orange as general European war spilled over into Ireland. He served at its head in the earl of Antrim's regiment during which time he saw two of his brothers killed and was himself severely wounded and left for dead on the battlefield of Aughrim. He was taken to prison in England and can be identified as a lieutenant in a list of Irish prisoners lodged at Soho Square in London in 1691 together with an ensign of the same surname who was presumably second officer of the MacLochlainn company. Diarmaid escaped to France after four years imprisonment where he became a lieutenant in the Irish regiment of Dorrington. During service in the war of the Spanish succession he suffered further wounds including a shot to the head at the battle of Malplaquet and eventually died from their cumulative effect at the siege of Landau in 1713. His widow petitioned the king of France for a pension to support their five children and was granted a pension of three hundred livres but no further trace of her or her children can be found in the records . An office copy of letters patent issued to Diarmaid in 1702 by James Terry herald to 'James III' the old pretender in exile at St Germain-en-Laye near Paris survives in the Cabinet des Titres of the Bibliothéque Nationale in Paris . The original would appear to have been copied after being submitted to the French authorities as a proof of nobility. The patent takes the form of a confirmation of arms in which Diarmaid is described as:
the first or chief of that moste antient and noble family of the MacLaughlins to wch belongs the foresaid Whitecastle of Inishone and the lands belonging to it
The patent recites a genealogy tracing the ancestry of Diarmaid to five generations on the male line with spouses being traced to families of note being 'MacGroddy of Desertegney', 'O Dogherty of Trien Sluight Shane', 'O Cahan of Limavady', 'MacNamee of Largone' and 'O Dogherty of all Inishowen':
Phelemy | Owen | Terrence | Owen of Whitecastle | Darby | Darby alive 1702 | Anna
With names standardised into Irish form and a thirty three years per generation chronology the genealogy can be seen to bear some resemblance to the genealogy given in the O Clery Book of Genealogies paragraph 321:
Patent Chronology O Clery 321 Chronology Felim Aibhne | | Eoghan Niall | | Torlach alive 1603 Torlach caoch son on pardon list 1602  | | Eoghan alive 1636 Eoghan alive 1602 | | Diarmaid alive 1669 Diarmaid alive 1635 | Diarmaid patent 1702 | Aine
The chronologies broadly synchronise and the name sequence Torlach>Eoghan>Diarmaid is otherwise unknown in the MacLochlainn genealogy so it would appear that the genealogy given in the patent is a continuation of the genealogy captured by O Clery in the previous century only degraded so that the names and positions of the earlier ancestors have become garbled . While this is something we might expect from an oral genealogy recalled in such attenuated circumstances we should also leave open the possibility that the genealogy was falsified in its earlier reaches in order to gain support through female alliances from the genealogies of other Irish emigres in order to achieve the required number of quarters . The office copy does not contain an illustration or blazon of the arms confirmed but they are presumably those given as MacLaughlin (pictured above) in a book of arms compiled by James Terry the issuer of the patent in 1712 . In theory confirmations were given only if the arms in question had been in use for the greater of three generations or one hundred years but as heraldry had never been widely adopted by the Irish before this time, as evidenced by the lack of a native corpus of heraldic texts/inscriptions such as gave rise to the distinctive native heraldries of Wales and the west highlands of Scotland (in which attributed arms were projected into the past and then quartered to visually represent a genealogy), it seems most likely that these arms were created anew in 1702 from emblems previously associated with the MacLochlainn clan  though their significance and meaning is now unclear.