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I REALLY want to see a typical Mistress/slave type scene

BUT the slave (a guy) is totally unaware the Mistress is trans

Natalie Mars is the mistress. she fucks him doggy but he just thinks its a strap on. it isn't until he's on his back as she rams his butt that he realises.

When he realises he's shocked and wants to eave but she just gags him then rams his arse and jerks him off until he cums. 

note; a good 30+ mins of sounding, BJ  that he's really into before the fucking/before he knows