Romania does not have marriage equality - but it must now recognize the rights of same-sex spouses.
Adrian Coman, a Romanian, and Claibourn Robert Hamilton, an American, married in Belgium in 2010, seven years after the country legalized same-sex marriage.
"Although member states are free to authorize marriage between persons of the same sex or not, they may not impede the freedom of residence of an European Union citizen by refusing to grant his or her spouse of the same sex, a national of a non-EU country", Wathelet said in his opinion.
A new ruling by the European Court of Justice has been announced which would require all EU member states to recognise the rights of same sex couples.
He noted that "the directive makes no reference to member state law in order to determine the nature of "spouse", even though that concept must be interpreted autonomously and uniformly throughout the EU".
The judge added that "the objective of protecting the traditional family can not justify discrimination on grounds of sexual orientation" and that "the concept of "spouse" within the meaning of the directive also includes spouses of the same sex". The case was later referred to the court.
The case will be decided by a national court or tribunal later this year - although judges generally follow the Luxembourg court's directives.
If Coman's bid is successful, the ruling would be controversial in Romania, where United States evangelicals have pushed a law to ban same-sex marriage.
Sophie in 't Veld, the Vice President of the European Parliament's LGBTI Intergroup, told PinkNews: "This is fantastic news and a landmark opinion for rainbow families!"
Wathelet maintains that European Union law defines "spouse" includes legal married partners of the same sex and makes no reference to member nations' definition of the word.
"Romanian citizens can not be divided into good and gay". It is one of six European Union countries with no legal recognition of same-sex relationships, along with Bulgaria, Latvia, Lithuania, Poland, and Slovakia.
"Granting the spouse of a union citizen a right of residence constitutes recognition and the minimum guarantee that can be given them", the opinion concludes.
Bulgaria, Latvia, Lithuania, Poland, Romania and Slovakia have no legislation on the matter - while Austria, Croatia, Cyprus, Greece, Hungary, Malta, Slovenia, the Czech Republic and Estonia all allow some form of civil partnerships.