A/N: This is an idea I have had for a while now. This isn't original, nor too well thought out, but think of it as a grimdark plotbuuny and you should do fine.

Anyway, this is the theory of: What if Sanguinius had a son? Well, since he was an attractive, charming man in a position of authority, and I doubt women would be too busy looking at Mortarion with goo-goo eyes, it wouldn't be impossible for lack of female interest.

So, how would he affect the Imperium? I'm making it so that he only appears in M41, long after dear ol' dad is dead. This means that he will be adapting to the new situation, and new enemies, than those in M31, the Tyranids, Tau and Necrons especially.

As to how he got there without being heard of; well, let's see...

"Commander Dante. I wish to speak to you in private, I have found many disturbing things on my travels." Brother Corbulo spoke evenly, calmly despite the news he had found.

He had just returned from a rather mundane Ork attack on the hive-world of Jurt, a few thousand light-years away. While there, the Bloodcaller had come under heavy fire from the Orks, resulting in dreadful damage to the Warpdrives. The damage was repaired by Brother Incarael, but even the Master of the Blade needed time to mend such things, so in that time, Brother Corbulo took the chance to study under the Magos Genetor, a geneticist within the Adeptus Mechanicus, in an effort to learn a method to cure the Flaw. While he was there, he learnt of some documents, said to be penned by the ArchAngel Sanguinius himself.

Corbulo had decided to look at them, and study their nature before he left. Within the dcuments were mentions of a child, possibly an Astartes, called Vermiculo, and a hidden chamber on Baal, somewhere near Angel's Fall. The documents spoke of Vermiculo being in the cave, of the relics Sanguinius placed in the cave.

The document's spoke of the Emperor Himself, visiting this cave, with Sanguinius and Vermiculo, and leaving 'a peice of Sanguinius' inside the cave. If this was true, then the cave must be found. Corbulo had taken the yellowed parchment with him, rereading the blood-red writing over and over, trying to discern any hidden meanings.

When the Bloodcaller arrived on Baal, Corbulo had made haste to Commander Dante's chambers, hoping to recieve an audience with the Chapter Master. Now he had been given the chance to retell the tale, he told Dante everything. The cave, and it's importance seemed to catch Dante unawares, even if the ancient warrior didn't show it.

"Is that so? I shall call the Chapter Command, then we can decide upon who shall search for such a location. If it is near Angel's Fall then we will need to act fast, the Time of Challenge shall soon be upon us, and after the casulties sutained on Jurt, I fear that it will be too important to delay.

"Very well then Commander Dante. As you think best." Brother Corbulo said, making the sign of the Aquilla before leaving for his own chambers.

Commander Dante was left alone in the great hall he had spoke to Corbulo in.

Primarch help us, what did you need to hide? Dante prayed, calling upon Sanuinius for answers. The great Angel didn't see fit to respond.

A/N: Well, there's the prologue. I will be continuing this, but updates will be slow. There is a way to speed up updates however, and it involves the text box below. Yes, this is the part of the fic where I beg feebly for reviews so; PLEASE! DON'T BE SHY! Anyway, to all you readers, bye!