The Big Three, the Greek Gods Zeus, Posiedon, and Hades, made a pact at tyhe end of the second world war not to have any more demi-god children. For the most part, they stuck to that. Yes, Zeus and Posiedon each had one child about half a century later, and Hades' kids had never actually died, but they hadn't had any other demi-gods. But... they did.
You see, there was one child, a girl, that was the child of all three of them. Now, this happened completely by accident, on a day when all three were in a bit of a snit, and fighting with each other. Again. There is such a thing as luck, and as I, the writer of this tale knows quite well, when three siblings (especially those of the same gender) fight, they tend to get a bit of bad luck. The Three had stormed off, and each had accidentally cut himself in some form or another before an hour had passed. The gods' blood fell from Olympus, falling onto the earth below.
The blood mixed and fell upon a young woman, who was on a short, two-day vacation with her husband, to get away from the war in their home country, Britain. She didn't notice the blood as it dropped lighter than rain onto her head, and it seeped into her skin, creating a baby inside of her. She and her husband spent their short time away from home sightseeing and enjoying thew peace, and one another's company.
So, when some months later the couple found that she was pregnant, they never gave a second thought to the timing. For you see, the husband was nearly completely unable to have children, and they saw their child as a blessing. They loved the prospect of their child, but his any sign of her coming from the enemy. It would not do to have their sweet little girl die before she had had her first breath of life.
They, Lily and James, their names were, loved their daughter dearly, and had everything prepared for her did not know Who the girl was, nor, exactly, just What she was, and she was believed to be the couples' own child. Until they went to have her placed as Heiress to ther Potter fortunes. That was when they found that their little Judida was not James' child. In fact, the father's name was blurred away.
Now, Lily swore upon her magic and her life that she had been faithful to her husband, but he beleived her before she did that. They decided that James would blood adopt the child, and it wouldn't matter how she came to be, she was their little Judida Sinead Potter-Evans. They were happy for her first year and a half of Jude's life, even after they were forced into hiding by some blasted prophecy. On Hallowe'en, 1981, Jude's mum and dad were murdered by the self-proclaimed dark lord Voldemort. The, well, he couldn't really be called a man after shredding his soul like cheddar cheese for a sandwich, could he?
Anyway, Voldemort attempted to kill little Jude, but the demi-god, scared, unwittingly called on the godly powers from her immortal fathers, rather than those of wizarding one, and brought down a bolt of lightning to block the Killing Curse, leaving her onlt with a scar upon her head. The Headmaster of the wizarding school, Hogwarts, quickly sent her to Lily's relatives in Muggle Surrey, plotting ways to train the girl up as a tool.
When Petunia Dursley nee Evans went to set out the milk bottles, she bit back a scream fit for a Bansidhe, and instead grabbed the bundle holding her adoptive niece, and slammed the door behind her. The letter from the old man her sister had so admired, if not trusted, was filled with vague words, and veiled threats. Furious, she slammed the door to the cupboard under the stairs, locking the girl inside. Bright green eyes, turned by the curse that killed her mortal parents, stared into the dark, watching intently.
For you see, there is another twist to our tale. Little Jude had lived through all of this once before, until she was seventeen and had defeated Voldemort for the last time, losing the only people she cared about with her victory. She had only found out that year that she was part-god, but she still did not know who her godly parent(s) was(were). All she knew was what she had learned to do over one short lifetime, and that if she wanted to live, Camp Half Blood was her best bet.
She didn't trust falsely barmy old Leaders.
She sent her memories back in time to her younger self, who should hopefully get through them by the time she was four. After that, Camp Half Blood should stock up on granola bars and whatever occupies four-years-olds.
The one and a half years old child yawned sleepily, already not trusting anyone with a white beard past their shoulders.
Poor Santa.