On one hand, Merlin may gain an ally in Morgana. But on the other hand, if Morgana has her own dark plans or is being influenced by other forces, she could use Merlin's revelation against him. His act of revealing his magic could also change the power dynamic between them. For instance, if Morgana feels threatened by Merlin's power, she may try to undermine him. Or, if she sees an opportunity to use his magic for her own gain, she could manipulate the situation to her advantage.
He could face Morgana's distrust if she takes his secrecy the wrong way. Maybe she'll think he has other motives for hiding his magic from her.
Merlin could face exile. Uther may not tolerate having a magic - user so close to him.
She might be shocked at first. Given that in the original story Morgana has her own complex relationship with magic, seeing Merlin's magic could stir a mix of emotions in her, like envy or a sense of relief that she's not alone in her magical abilities.
He might face distrust from Morgana at first. She could think he has been using his magic against her without her knowledge.
Well, he might feel extremely lost and confused. He has been so used to relying on his magic for everything. Without it, he could face danger more easily as he no longer has his magical defenses. Also, his friends might have to step up more to protect him.
A fanfiction could focus on the relationship between Mordred and Morgana. It could explore how Mordred came to be so loyal to Morgana in the first place. Was it out of fear, admiration, or something else? And how does Merlin fit into this complex dynamic? He might be seen as an outsider trying to break their bond.
In some fanfictions, Prince Merlin (assuming he has some sort of princely status in this AU) and Morgana might be forced into an alliance against a common enemy. Maybe an ancient evil that threatens Camelot in a way that neither of them can face alone. They would have to put aside their differences and work together, which could lead to a slow - burning romance.
One consequence could be that his enemies might target Gordon to get to him. Since Gordon now knows his identity, if the bad guys find out, they could use Gordon as a way to harm Batman.
She could be shocked at first. After all, Merlin has been hiding his magic for so long. Maybe she feels a sense of betrayal initially, but then she might see an opportunity to have an ally in the world of magic.
Well, it might lead to him being ostracized in some communities. Since he can't hide his magic, in a society where magic is feared or not fully accepted, people could shun him. This would make it difficult for him to have a normal life among non - magic folk. Also, it could potentially expose Arthur, his friend, to unnecessary risks as his association with Merlin becomes more obvious.
One possibility is that there would be a great deal of tension. Old Merlin has seen so much and has his own wisdom, while Morgana has her own powers and motives. Maybe Merlin would try to persuade Morgana to abandon her dark path. He could use his experience and the bond they once had to appeal to her better nature.