Some tellings of Arthurian mythos say that the greatest warlock to walk the Earth and personal mentor to the Once and Future King experienced time backwards. (I don't really get it, but it worked in The Sword and The Stone cartoon, right?)
Hundreds of years post Arthur's death, Merlin finds himself reliving his time with Arthur, starting at their first street fight. Maybe this is his chance to change things! Maybe he's just finally lost his head and isn't back in time at all. Maybe someone just wanted to give Merlin more time with his soulmate.
Whatever the case, Merlin knows one thing: LAST TIME DIDN'T WORK! Hiding his magic and protecting Arthur from behind the scenes DIDN'T WORK! So this time he's going in blazing. Armed with magic he has perfected over centuries and a loyalty that could take out the Saxons AND the Huns, he will do everything to protect Arthur - just like he always has! What's Uther gonna do? Kill him??? Good luck, you open can of flat Mountain Dew, our boy is IMMORTAL!