A EU country must approve the change for a person who has changed gender and name in another EU country, states the EU court in a recent ruling.
"A member state's refusal to recognize a legal change of gender identity in another member state hinders the right to reside and move freely", it says in Friday's ruling.
Concretely, it concerns a case where a person with British and Romanian citizenship has been recognized as a man in the UK, but was then denied by the authorities in Romania when he wanted to change his first name, gender, and personal identity number there as well.
The fact that the UK has left the EU does not see the court as an obstacle, since the changes were made when the country was still a member.