Cimmeriac

The Cimmeriac were a little-known xenos race from the Eastern Fringe.

Facing the Tyranid invasion of Hive Fleet Jormungandr in the late 41st Millennium, they accepted the uneasy truce proposed by High Admiral Vortigern Hanroth to join his loose alliance of various fleets with their Shadowcruiser starships.

In 995.M41, during the subsequent Battle of Black Nebula, Hanroth and his unlikely allies shattered Hive Fleet Jormungandr.

Nevertheless, less than five Terran years later Hanroth himself would lead the obliteration of the Cimmeriac civilisation in the name of the Emperor, proving once again that despite all the HFY! Imperium and Chaos fans love to rub in the faces of Xenos players, in the end even the "good guys" of the humans are scumbags who are willing to kill those who fight beside them for their own gain. Although, having fought beside each other doesn't make each other allies or friends and it's childish to think otherwise. Besides, considering how the Imperium generally ignores aliens that aren't a threat, they probably deserved it or it was otherwise necessary. Or they got very unlucky with which Imperial was in charge that day. Plus, if "truce" is the correct term here for their alliance, then they were already at war in the first place and just stopped shooting each other to shoot the Tyranids and then went back to shooting each other.