By Sandi Sidhu and Lauren Said-Moorhouse, CNN

(CNN) -- A gay Singaporean doctor has won the right to adopt a child he fathered in the United States through a surrogate, in a landmark ruling for the socially conservative country.

On Monday, Singapore's High Court overturned a 2017 ruling in which a district judge said the man could not legally adopt the child because he was conceived through in vitro fertilization -- a process limited to heterosexual married couples in Singapore -- and brought to term through surrogacy, which is technically banned.

Under Singapore law, children born out of wedlock are considered illegitimate and do not have the same rights as those born to married couples, unless legally adopted.

The 46-year-old doctor, who has not been identified, had been fighting to legally adopt his son, now 5, in an effort to acquire citizenship for the boy and secure his long-term residency in the city-state.

The man and his long-term partner -- who have been together for around 13 years -- paid $200,000 for the overseas surrogacy services after being told by local agencies that they were unlikely to be approved as adoptive parents because of their sexual orientation. The man's sperm was used to fertilize an egg from an anonymous donor and the egg was then transplanted into the surrogate mother.

Same-sex marriage is not recognized in Singapore while sex between men is punishable by up to two years in jail.

After the child was born in Pennsylvania in 2013, the surrogate mother -- a US citizen -- relinquished all parental rights and the man returned to Singapore with his son, court documents revealed.

In delivering the court's judgment, Chief Justice Sundaresh Menon emphasized that the ruling "should not be taken as an endorsement" of the man's actions.

He said the court attributed "significant weight to the concern not to violate the public policy against the formation of same-sex family units."

But he added: "The evidence has demonstrated to us that it is very much in the interests of the Child that the adoption order be made, having regard principally to the fact that his prospects of acquiring Singapore citizenship could be significantly enhanced."

After the historic decision, the man told CNN in an emailed statement that the legal process had "been a long and difficult journey for our family" but "we are happy and relieved with the High Court's ruling."

He continued: "We hope that with the adoption order, it will increase the chances of our son residing in Singapore for the long term. Singapore is the only place we have known as home, and is where we wish to raise our family. We would like to thank our family, friends and the community for their support and encouragement. We ask for privacy during this time so that our family can celebrate the holidays."