Just a note on the comment above, " I understand that the "rightfu' king" in this case is not Bonnie Prince Charlie, but his father."

It's not his father but his grandfather, James VII and II. James II, who was Catholic, became King in 1685 when his brother Charles II died. At first, the people supported him, but James kept bringing in Catholic officials. People still accepted him, because his heirs, his daughters Mary and Anne, were protestant.

Then James's (second) wife bore a boy, who would have been James III. At that point, the Glorious Revolution began. (I oversimplify dramatically.) James III was the Old Pretender. His son was Bonnie Prince Charlie, the Young Pretender.

The author of this song is disputed, but since it takes place on "The Irish Shore," it's about James II and the period around the Battle of the Boyne.