Castellucci described the experience of trying to obtain legal documents listing them as non-binary as an "ordeal" and the court heard they worried about possible difficulties related to their gender identity when applying for British citizenship.
They also raised concerns about how their gender identity would be reflected on their death certificate, when their US documents state they are non-binary.
Lord Justice Singh, sitting with Dame Victoria Sharp and Sir Andrew McFarlane, said that only 11 countries worldwide, as well as some US states including California, recognise non-binary gender in law.
Non-binary is an umbrella term for those those who do not identify as exclusively male or female.
In a judgment published on Tuesday, external, Lord Justice Singh said: "The concept of 'gender' in the Gender Recognition Act (GRA), when referred to in the context of the domestic law route, is confined to two genders."
Legally there are only two possible genders in the UK. So now can we teach kids in line with the actual law?
We have to adhere to the law in the US if we visit or live there. The audacity of demanding the law in another country is changed just for you is pretty staggering.
And his dead body will still be a male skeleton, with male DNA...