Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150112024430/@comment-86.159.94.118-20150805195136

I suppose there exists the possibility that the Blood Ravens may be a loyalist splinter from one of the traitor legions. We know for certain that not all loyalist legionaires in the traitor legions were killed by Horus and the other traitor primarchs so this is a strong possibility.

The grey knights themselves were formed from loyalist astares of traitor legions so there is a possibility.