Even after revealing his magic, helping repeal the ban, and being (unwillingly) made Court Sorcerer, Merlin never tells anyone about Freya. Not in the sense of actively keeping her a secret, but just...not mentioning it. When he's working, then he is working, and even though he's trying to be more honest, he's spent 10 years keeping secrets, so he doesn't just volunteer information. If he's asked, he'll answer, and it'll probably make sense, but it's kind of like trying to pick the right responses in a dialogue tree.
One day, the Round Table knights are out "on patrol" (a.k.a. fucking around in the woods) and a whole woman just. Comes up. Out of the creek they're sitting by. They know she's a sorceress of some kind because a) she walked out of a creek that is knee-deep at most and b) is still completely dry, but Merlin doesn't look surprised to see her, so she must be okay.
She doesn't really acknowledge them beyond a glance and a little nod (it's only been a year, they're working on trust) but she smiles at Merlin and gives him his Sidhe staff ("You left it in the still room. Again."/"Oops?") and says she'll see him for dinner tonight, and then she walks back into the creek and is gone.
The knights have Questions. Who is she, how did she do that, where did she come from, where did she go, why is Merlin leaving his staff in her still room (shut up, Gwaine), why are they having dinner? But they'll have to take baby steps to get there.
Elyan: Who was that?
Merlin, paying maybe ¼ of an attention: Freya.
Percival: And how did she...?
Merlin, tying the staff to his saddle: She's the Lady of the Lake.
Gwaine: And you're having dinner with the Lady of the Lake?
Merlin, unpacking lunch: Mm-hm.
Leon: Why?
Merlin, peeling an apple: Uh, because she's my wife and I like being with her?
The Knights:
Arthur, voice cracking: She's your