The Khan's relationship with Malcador was... a little awkward.
The Khan had been close to Horus, largely thanks to Malcador taking the blame for everything.
Even before his corruption, Horus had seen quite a few of the Imperium's hidden problems. But he personally revered the Emperor, which led him to believe that Malcador, the Perpetual who had always stood beside the Emperor, harbored some unspeakable secret.
The Emperor was always righteous! That scheming old bastard Malcador must have been hiding some plot from him.
The Warmaster thought Malcador was a villain who secretly stabbed the Primarchs in the back. The Khan knew those decisions had, of course, been made jointly by Malcador and the Emperor, but he never said so.
You had to stroke a stubborn mule the right way.
So the Khan and Horus usually bonded by cursing Malcador together.
Later, after trading his life for that of Mortarion, Nurgle's prince, in the Imperial Palace, Malcador and the Emperor had brought him back. Only then had he truly understood their power.
The Khan had always felt somewhat guilty toward Malcador, that hero of the Imperium. During the few times he had met Malcador while the man was alive-returning with Horus-he had hardly ever shown him a pleasant face. When Malcador requested help from the White Scars, his attitude had been, "Hello, the subscriber you have called is outside the service area..."
It was not until the defense of Terra, when the Khan traded lives with Mortarion and Malcador and the Emperor revived him, that he understood just how terrifying Malcador was.
The Khan believed that all the Primarchs owed Malcador a debt. They simply no longer had any chance to repay it.
As for the precious legacy Malcador had left behind... if it needed beating, he would still beat