This may be a bit of a stretch but
In “the Fables of Doom” Cassandra was temporally (unsure about that part because at the end it looked like she kept some of the magic) Merlin
And last episode she was saved by The Lady of the Lake (or what seems to be the main one)
And in the legends Merlin and The Lady of the Lake were in a relationship
So unless we specially see Merlin, Cassandra and The Lady of the Lake might be a couple