Anyway, you might be right. This is from 2x11:
Gaius: The Druid boy? What's he doing here?
Merlin: He was guiding someone to Morgana's chamber.
Gaius: Are you sure? She and the boy had a kind of bond.
Merlin: Yeah, but this is about more than that.
Gaius: What do you mean?
Merlin: What if they'd been caught? Whatever they were doing, they were prepared to die for it.
So it looks like Morgana was also using her telepathy to give Mordred instructions to reach her room. I don't remember seeing that though but I reckon that it's not one of my episodes of choice to rewatch.
Wow, quite some digging on Druids and telepathy we did here thanks to Daegal!
Arthur is knocked unconscious or prevented from knowing about Merlin's magic:
-He is looking down to the peace treaty when Merlin diverts the trajectory of Albinâ€™s arrow.