Help with story (incest/accident)

[cryingtable]

I need help finding a story with a somwehat strange twist.
The story starts out with a guy pinned to the bed by his mother one day, in a tickling game. She was wearing no undies and eventually the guy entered his mom. He tried to grip her, but she gave him a look and he stopped. They continued playing, with him inside her, she acting oblivious and they continued til he came.

Thanks in advance.