Hey guys, what if The Emperor let Horus kill him because he fell to Chaos as well? No one knows what happened on Horus' ship, right? What if he lowered his shields to let The Emperor on board so he could corrupt him and while he was doing that Sanguinius stumbled upon them, there was a fight, Horus allowed himself to be killed after The Emperor killed Sanguinius, but was also mortally wounded. So now he is stealthly influencing the Imperum for Chaos since he's their best link to the material world.