Now, something important to note. “Sidhe” are Irish fairies said to live in hills or fairy mounds. They don’t live in mounds in Merlin of course, however their differences in this versus the folklore are made up for in their similarities — in that they’re of magic kind. And a powerful magic at that.

I think it’s safe, then, to deduce that they’re born with immortality? Or perhaps they’re born in mounds, and move to Avalon at some point where they become immortal? Yes, I might like that idea better.

Point is, at some point, somehow, they’re immortal. And I’ll bet that only those born of magic can be granted said immortality.

Now comes Merlin and Arthur; in the finale. Yes, the very bitter end.

During the finale, Merlin tries to bring Arthur to the lake of Avalon (or rather, the tower amidst it) where he might heal him of his mortal affliction.

Arthur is a mortal prince.

Merlin is a person born of powerful magic.

You see where I’m going with this?

We all know that Arthur dies before/when he arrives at the lake of Avalon (canonically, when they rue in Kilgharrah’s back if I’m not mistaken), and — eventually — Merlin has to send him off.

My point is, what if by sending him off to the lake, he offers Arthur’s souls to the sidhe or the Triple Goddess or whoever is “running” this lake; and thus Merlin is granted immortality.

Meaning that Arthur’s death isn’t only the thing that killed Merlin (metaphorically speaking, but technically that was his other half so—), but is also what made him live [for so damn long].

But I’m not done yet.

Because Arthur is also, technically, born of magic. It makes me wonder what would’ve happened had he been healed. Would he have had to offer up his own soul or else his physical form would perish, and he thus is under the sidhe (or whoever’s) control as part of a new arc after the finale? Would that grant him immortality?; thus making him a Once and Future King different than we know that statement to be?

Would Merlin then remain mortal; or again, was he really immortal all along?