Andy Smillie
The Herald of Sanguinius

Crowned as the new Emperor of Imperium Secundus, Sanguinius of the Blood Angels faces the very real threat of betrayal from within his new realm.
The Horus Heresy
short

Also in:
Imperium Secundus
Legions Divided Quick Read Collection
Echoes of Imperium
The Horus Heresy Audio Drama Bundle 2015
Eye of Terra