As Maulik V pointed out in a comment, and as this ELU link perfectly explains (and because I don't have enough rep to post only a comment when a comment is due), you can refer to this person as

they

as in

singular they

which despite not being taught in schools around the world, is perfectly valid for referring to a single person.

As Maulik V pointed out in a comment, and as this ELU link perfectly explains (and because I don't have enough rep to post only a comment when a comment is due), you can refer to this person as

they

as in

singular they

which despite not being taught in schools around the world, is perfectly valid for referring to a single person.