The Sanguinor: Exemplar of the Host is a short story by James Swallow. It was published online in December 2013 as part of the Black Library Advent Calendar (2013).
For seven years the Blood Angels have warred against the Great Devourer on Skylos. For seven years they have fought and bled and died. Now, the war is almost over, and only a handful of the sons of Sanguinius remain. As they prepare to make their last stand, thoughts turn to the Sanguinor, said to arrive and bring hope in moments of great peril. But the Sanguinor is just a legend. It isn't real... is it?