Aodh was right in saying that this song was about fighting the French (math agad, 'Aoidh) - it's from the Napoleonic wars; the King's son is one of the sons of George III. This is very obvious if you have the second verse (the first if you count Tha mi'n duil etc as a chorus not a verse) which is missing in Philippa's version posted above. I don't have a copy of An Duanaire and don't have access to one where I'm living now (a few thousand miles from home), but my notes tell my that the song is number 71 in that book. If someone can get to a major library in Scotland (or, probably, to the local public library in Stornoway) they may be able to find it and post the words given there; an Duanaire would also give some indication of whether the author is known. In case no-one does that, I'll post the words that I have in a separate message.

The English verse about "when we came back to the land" is nothing to do with this Gaelic song, it's an addition by the "translator"; there were no evictions by fire-raiser in Skye (where this song comes from) at the time of the Napoleonic wars, so it's rather inappropriate. It may be based on something from a rather later Gaelic song, one of the songs made in the aftermath of the Crimea war (many of those who stood in the famous "thin red line" did indeed come home to find their families evicted).