Would the Allies have to cooperate with Stalin if he joined their war?

Would the Allies have to cooperate with Stalin if he joined their war?

They would face the problem of explaining why they refused to work with a state that had joined their war and sent representatives.

Stalin could complicate Allied diplomacy simply by declaring that the Soviet Union was joining the war against their enemies. Sending representatives would turn cooperation into an immediate political question. The Allies would then face the difficulty of rejecting a government offering to fight on their side.