78. LED Selection & Failure

Question.1

Tony is using a Vishay TLDR6400 (5 mm Red LED).
DigiKey part: Vishay TLDR6400

He connects it to a 12 V AC source using a series resistor calculated to allow 10 mA RMS current.

Red-LED-AC-circuit

However, after some time, the LED becomes permanently damaged.
What is the most likely reason?

 

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