"Rape: unlawful sexual activity and usually sexual intercourse carried out forcibly or under threat of injury against a person's will or with a person who is beneath a certain age or incapable of valid consent because of mental illness, mental deficiency, intoxication, unconsciousness, or deception."

Source: https://www.merriam-webster.com/dictionary/rape

The key point being "valid consent" and its contravention by deception. i.e. It's not valid if what you are consenting to is a lie, namely who you think you are having sex with.