Is it safe to assume that the Sorcerer is the mysterious daddy of Maleficent's child ?
First, Mal is immortal (confirmed by Adam & Eddy). And before everything happened, there was Merlin. And now, they should find him to fight the darkness. That means the Sorcerer is possbily immortal too
Second, he is the most powerful wizard in the world (even stronger than the Dark Ones). I think he can turn into a dragon too
Third, I find it strange when the Apprentice met young Lily on the bus. Of course, he could felt sorry for her so he told her everything. But who knows ? Maybe Merlin have his Apprentice help his daughter understand things
Fourth, almost everything about the Sorcerer and the Apprentice somehow connects to stars, from the hat to the Star Publishing ... That's why the star birthmark on Lily's wrist somewhat got me thinking ...
Finally, when they introduce some "mysterious missing characters", they will usually be the same person. For example, Henry's dad and Gold's son, Emma's friend and Maleficent's child, ... Now, they have to find "the Sorcerer" and "Lily's dad". Hmmm ....
Therofore, there's a high chance that Merlin is actually Liliy's father