Sigh. I really fail to see how this is a matter of "opinon" on this wiki.
The hand was NOT Lancelot's or Arthur's. (What's next? Someone notices the arm looks a little darker than the arm in The Coming of Arthur and suggests it's ELYAN? Come on, really, people?)
The show's writers/director already confirmed it was Freya's hand. A LONG while back. But they supposedly used a male diver for that scene, and that's the ONLY reason it appears to be a man's arm. But that doesn't make it Lancelot or Arthur.
And Merlin is NOT the only King Arthur take to use a male-looking arm for The Lady of the Lake. I've even seen BOOKS of the legend where the arm is drawn in an overt masculine way. But that doesn't mean in those books, where Lancelot was living as a monk or in France or wherever because of being exiled, he suddenly appeared in the lake and took back the sword. Ditto Arthur.
This fustrates me because this wiki is supposed to keep the facts straight. This isn't fanon. If you people want a story about it being Lancelot or Arthur's arm, go write one and post it on FF.net, yes?
I've even had to deal with strong opinoned people who think it was Arthur's hand "fixing" carefully edited info pages I did a lot of work on in this wiki in the past.
This isn't a pairing debate left open (aka, did Agravaine love Morgana, were Sefa and Merlin a couple before season five? etc...). This is a concluded fact that was confirmed a long while back.
If I may quote (possibly misquote, since this is from memory) Kilgharrah: "There is no right or wrong, there's only what is and what will be."
It IS Freya's arm, and still WILL BE the next time someone brings this 'topic' up. LOL.
Hengist? Bah! It's not Hengist. The arm is OBVIOUSLY Will from The Moment of Truth! Freya felt so bad about all of Merlin's friends dying (including herself) that she transported Will's spirit to Avalon ASAP after she became the Lady of the Lake. Sadly, she forgot that Merlin had RUN OUT of Avalon water and the fisher king was dead and thus could not give him any more. So, to make up for the fact that he didn't get to see his friend again, because she hogged the scrying super magic puddle Avalon-style skype in The Coming of Arthur, she allowed Will to be the one to take back the sword!