Conversation so far:
Who was Julian in relation to Constantius II?
Julian was Constantius's last surviving cousin.
Who promoted Julian to Caesar under Constantius II's time as Roman Emperor?
In 355, Constantius promoted his last surviving cousin Julian to the rank of Caesar.
Who was the first usurper to try to take power from Constantius II?
The first usurper to try to take power away from Constantius II was Magnentius.
What was the result of the revolt in Gaul for Constantius II?
Silvanus had surrendered to Constantius II after the Battle of Mursa Major. Constantius had made him magister militum in 353 with the purpose of blocking the German threats.

Question: Who was the next to attempt to usurp Claudius II's power?
Self-contained rewrite: Who was the next to attempt to usurp Claudius II's power?