It was under fraudulent conditions. I would never had been willing had I had known that they were transgender beforehand. The transgender person lied in order have to have sex with me, that my friend is sexual assault. Its called rape by deception.
It centers around consent, remember you cannot have sex with someone without consent or it is rape.
Rape by Deception | Psychology Today
"Deceiving another person in order to have sex with them is morally wrong when it prevents the other person from giving fully informed consent to the act (Rubenfeld, 2012-2013). The reason for this is that informed consent cannot be given when you don't really know what you agree to when agreeing to have sex."
The character in the OP is a sexual predator.
"Sexual encounters involving deception that may qualify as sexual misconduct include (among many others) lying about the use of contraception, lying about your age, gender, marital status, religion or job, lying about having been tested for sexually transmitted diseases and infections, pretending to be someone’s partner, and falsely making the partner believe that the sexual act is a medical procedure."
Here is a good legal conversation on the subject:
Solving the Riddle of Rape-by-Deception | Yale Law & Policy Review