I have just discovered a new proof of the existence of God.
Consider the following sentence:
(S) If this sentence is true, then God exists.
Suppose sentence S is true. Then the first clause is satisfied, so the second clause is true. Thus, God exists.
What the preceding paragraph proves is that if sentence S is true, then God exists. But that is exactly what sentence S asserts. So that means we have proved that sentence S is true! And therefore God really does exist.
As a result of this proof I am longer an atheist. Sorry to disappoint everyone.*
* Note this proof also works for unicorns. Yay, unicorns exist!