I experienced a wet dream during the fasting hours in Ramadan. Do I have to make up the fast?

God ordained fasting as evidenced in the Quran, “And whosoever of you is present let him fast the month” (Quran 2:185). Fasting is one of the acts of worship whose rewards God has made known only to Himself and to no one else.
Yet, man is subject to forgetfulness, prone to error and sleep, while God, Most High, is not taken by fatigue or sleep. One of His mercies to His creatures is removing the sin for mistakes, forgetfulness, and for actions that they were coerced into performing. The Messenger of God (peace and blessings be upon him) clarified that the Pen [used to record deeds] is lifted while one is asleep. He said, "The pen is lifted from three: young children until they reach puberty, the one who is asleep until he wakes, and the one who is insane until he comes to his senses."
We can clarify from the above that the Pen (and therefore the deeds it would record) is lifted for the person who is asleep, so he is not held accountable for whatever happens while sleeping.

The Ruling
Anyone who has a wet dream during the fasting hours of Ramadan has not sinned, and does not need to make up the fast day.

And God Almighty knows best.