Which Drennan family line are you descended from? were your ancestors from Scotland, the west of Ireland or Ulster? it would be nice to link in with some other people's research as i have only recently begun researching this surname..
Descended from Heremon....sounds a great story but im afraid that he was a legendary king and the milesian line of kings is regarded as being very suspect by expert scholars,the lineages of these kings were first written down in about 450- 1000AD and were manipulated for political reasons between the many ruling dynasties of Irish Kings....if you want proof then just compare the lineages in the major manuscripts such as the the 4 masters, Ulster or several other major annals then you see some glaring inconsistencies due to political manipulation of history...at any one time in Ireland up until the 1500s there were many Kings...these were vassels to Over Kings who theoretically answered to a high king but in fact paid only lip service to the high king ...The first "authenticated" historical king of Ireland was Nial of the nine hostages who is recorded in romano-British sources in the late 400s and who appears to be the ancestor of the great O'Neill dynasties of Ireland who were also high kings for sometime... its a great story but all history is subject to spin and without documentation it's only a story, even although its alovely one...
if i had to take every story about my various ancestors being Kings then I am very Royal indeed, out of about 64 surnames I am researching I have only found conclusive links to Royalty in one of them, but i dont care because all these people from many walks of life contributed something to creating me and for that i am thankful and it is enough for me to know who they are and pass down their memory to the next generation of my family
am not doubting your commitment and dedication to research nor your abilities therefore if you have this evidence with the manuscript sources clearly listed and detailed then I know that the Lord Lyon's heraldic court and the Herald of Ulster(traditional High Herald of Ireland)as well as the National Archives/National Museums in Dublin, Edinburgh & London would kill for such a gem as information like this is extremely rare...if you like I can provide the addresses and contact details of the many establishments and you could contact them..I would love to see family research like this being published
as a footnote, there has been some very exciting evidence unearthed by DNA comparison of people who were born of Irish families in the west of ireland and who bore Irish surnames with another group from Galicia spain(traditional cetlic-iberian area) and the scientists discovered some matches which indicate that the Milesian legends of the "Irish" coming from spain may be correct after all..heres the news articles listing the source of the research.very exciting stuff