He remembered the clothing of these guys very well. At some point in the past, they were a force to be feared within the Kingdom and protected the previous King. They were known to all as 'The Royal Executioners', but after the previous King's fall and Sariel II's rise as King, the group disappeared.
At the time, they were a group feared even by him, as they were cold-blooded killers who dealt with any traitor or malicious person who wanted to oppose Sariel I, the former King, or his family.
Despite all that and the fact that they were feared in the Kingdom, after the fall of Sariel I, the group disappeared, and many of them were killed; Ronan himself witnessed it and participated in some of the missions to kill them.
Even so, once Ronan heard a rumor.