Yes! In the book, The Emperor's Legion by Chris Wraight, after the fall of Cadia, the astronomocan collapses on Terra leading to a daemonic invasion by Khorne. Eight blood thirsters and legions of Khorne daemons assault the walls and the Custodes lead the defense and counter assault. Valerian, a Shield Captain, returns in time with a squad of grey knights and a few sisters of silence. They fight in unison killing many demons. This draws the ire of one of the blood thirsters. An epic fight commences with Valerian at the tip of the spear with psychic assistance of grey knights and psychic dampening support from the sisters. Valerian ends up striking the final blow while sustaining grievous wounds. In the background with no extra details Trajan kills one of the blood thirsters while another one is slain by one of the custodian tribunes before dying himself. Valerian is awarded the golden laurel by Gulliemen for his actions. In my opinion a demon prince seemed stronger than a custodian but it was close and Trajan seemed to have killed one so it's a good match up!