Board Thread:Warhammer 40k General Discussion/@comment-24944355-20140706083220/@comment-25149066-20140707161236

The Red Thirst would have been a perfect way to corrupt Sanguinius though I think the Process would have taken longer and he would resist for a while.

If Sanguinius was the Warmaster of Chaos I would be willing to believe that Horus would have been on the Loyalist side.