Specific mother/son mind control story

[xMysterious1x]

Hello all. I am looking for a story I read a few weeks ago involving a son who finds a trigger word that makes his mother fall into a trance. He then proceeds to take advantage of it and eventually has sex with her. After they are finished, the sister walks in and the mom, embarrassed leaves. Then he tries using the word on his sister.

Does anyone know what story this is?