Maybe it's a new character introduced just for this plot twist. This would add an element of mystery and new drama to the story.
There's also a possibility that it's a character from her past that she had a brief encounter with. This would create a whole different set of conflicts and storylines, like dealing with unresolved feelings and the shock of the unexpected pregnancy.
Or, in a more creative take, it could be a new character introduced just for this fanfic. This new character could bring a whole new set of dynamics and storylines, like a mysterious stranger who has some special connection to Clary.
Jace could be the father. Since they have a strong connection in the original story, it would make sense for him to be the father in the fanfiction.
The Seelie Queen could be an antagonist. She might see the unborn child as a threat to her power or a valuable asset to control. So, she could try to manipulate Magnus and Clary throughout the pregnancy.
The 'Clary is pregnant fanfiction' might have a plot where the pregnancy is unexpected. Clary could be in the middle of some important events in her life, like her career or studies. Now she has to re - evaluate everything. Her friends and family may have different reactions, some being supportive and some being worried. This could lead to a lot of emotional turmoil and character development for Clary as she navigates this new phase of her life.
It could also be someone new, a character created specifically for the fanfiction. Maybe a powerful new demigod who catches Annabeth's eye, and their relationship leads to the pregnancy.
It could be a long - lost love from Mavis's past. Maybe someone she thought she'd never see again but who re - enters her life right before she discovers she's pregnant.
It could be another powerful magical being in her realm. Maybe a long - time ally or a mysterious figure that has been in the background of the story's world. This would add an element of mystery and intrigue to the fanfiction.
In some fanfictions, the father could be a human character. This would add an interesting dynamic as it would involve dealing with the differences between a human and a Digimon in a relationship and during pregnancy. It could also lead to a story about acceptance and dealing with the unconventional nature of such a union.
It could be one of her close friends or classmates in 90210. Maybe someone she had a brief fling with during a party or a school event.
It could be Ron. Since they have a relationship in the original story, it's a very likely option. Their relationship could be further developed as they face the new chapter of becoming parents together.