The Four Dragon Kings, the Red Dragon King.
On the very first day of arriving in Beijing, he was poisoned to death.
As for who exactly killed the Red Dragon King, there is no concrete evidence pointing to anyone, but everyone in Beijing knows who holds a grudge against the Dragon Sect and has the capability to eliminate its members.
The answer isn't hard to deduce; everyone believes that no one other than Song Yun would have done such a thing.
Although many quickly speculated that Song Yun was behind it, nearly everyone was still quite shocked by the incident.
To openly kill a Dragon King on the street cannot merely be described as bold; it's an unmistakable declaration of war. Although a battle between the Shura Alliance and the Dragon Sect was inevitable, the timing and initiator of the war were profound questions. No one expected the traditionally passive Shura Alliance, which adhered to the principle of not provoking unless provoked, to ignite the conflict at such a moment.
