The Source's Heir

The Unborn Source was the unborn son of Cole Turner and Phoebe Halliwell. He was the first Demon/Witch Hybrid. The union between Cole, who was at the time possessed by The Source of All Evil, and Phoebe, who is a Charmed One, created a massive concentration of power. Even as a two month old fetus, he was able to produce great amounts of magic. Against this power, even the strongest of demons perished. He would have been the first born of the The Charmed One, Phoebe Halliwell, if he had survived.

Pre-conception
Shortly after The Source of All Evil completely took over Cole, the Seer told him that she had foreseen Phoebe giving birth to the most powerful magical child ever conceived at the time. The child would have been born as a powerful good witch had Phoebe married The Source/Cole in a white wedding. This act would have ended any chance of The Source/Cole being officially crowned as The Source. However, The Source/Cole tricked Phoebe into marrying him in a dark wedding. This ensured that the child, who like Belthazor/Cole, was part demon, had an evil nature that could be easily tapped into. In doing this, The Seer ensured that the child would not be heir to the Charmed Ones' destiny.

Conception
The Seer had The Source/Cole slip Phoebe some chocolates enchanted with a tonic she brewed, which enhanced fertility. These measures not only ensured that the child could be conceived easily but also that the child's evil evil nature would grow stronger. After Cole/Source was officially coronated as the Source of All Evil, he had the Seer give Phoebe a tonic made from her blood, both daily and nightly, so that it not only strengthened the baby's demon side, but also slowly ate away at Phoebe's good side.

Under his influence, Phoebe began manifesting the powers of the Queen of the Underworld, and was able to touch the Grimoire, even though she never became fully evil herself.

Truth and death
"But you have no direct lineage to the Source by blood or by magic."

- Dark Priest

"I know. It's not me and it's not Cole, it's the Source."

- Phoebe

The Charmed Ones thought that once Phoebe renounced her crown and got the baby away from evil influences and the tonic effects, they'd be able to turn him good. Unfortunately, after The Source/Cole was vanquished, the evil essence of The Source possessed the child, like it did with his father Cole before that. Once in full control of the baby and it's powers, it was able to control his own mother from the womb. He forced Phoebe to hit Paige twice, as he blamed Paige for foiling his father's plans. He was also taking a considerable physical toll on Phoebe as well. She soon realized that the baby contained nothing of her or Cole but was the Source itself.

The Seer lured Phoebe into the Underworld and magically transferred him from Phoebe's womb to her own as part of her bid to become the new Source. She told Phoebe that the baby was never hers nor Cole's to begin with, that, from the moment of conception, the baby had always been hers. Immediately after, Paige expressed her sympathies for the loss of the child, but Phoebe told her it was ok, because the child never belonged to her.

With the baby in her womb, the Seer took the oath to become the new Source, fulfilling her own centuries-long ambition of becoming ruler of the Underworld. As her first act, she intended to sacrifice the Charmed Ones as part of her coronation. However, she soon discovered that, much like with Phoebe, the baby's powers were too much for her to handle. The sisters noticed this, and used the Power of Three Spell to force her to tap into all of the baby's power, vanquishing every demon in the room -- including the Unborn Source, as he wasn't old enough to handle all the force of his powers yet.

The Prophecy of the Twice-Blessed Child
The child was conceived little earlier than Wyatt Halliwell. Seeing as how the Unborn Source and Wyatt were conceived at relatively the same time, it is possible that the child of Phoebe and Cole would have been born right on time during the night of the Wiccan Festival of Lights and the Aurora Borealis, and would have been the prophesied Twice-Blessed Child. In an alternate reality created by Cole, The Seer foresaw that Phoebe and Cole were to produce a magical child. Seeing as how Wyatt wasn't born in that reality, the child of Phoebe and Cole would have possibly been born as the twice blessed child. Just like Wyatt, the child possessed great and numerous powers. Kyra was able to manipulate circumstances to change the future. The Seer most likely have done the same thing. She foresaw a powerful magical child between Phoebe and Cole. And then she changed/manipulated certain circumstances so the child would be evil instead of good.

Powers and Abilities
He possessed numerous powers from the womb as listed below. He most likely possessed all of the powers the Source and some powers from his mother's side, as well as some unique to him. As a demon-witch hybrid, he also possessed the basic powers of a witch, such as spellcasting, potion making and scrying. If he had been born, his powers would have been even more developed, and he could have been one of the most powerful witches. There is possibility that he was even stronger than Wyatt.
 * Fire Throwing
 * Advanced Fire Throwing
 * Fire Balls
 * Flaming
 * Sensing
 * Telekinesis
 * Electrokinesis
 * Telepathy
 * Super Strength
 * Possession
 * Transformation
 * Immunity (possibly)
 * Immortality (possibly)
 * Warren Inherited Powers
 * Every power of the Source