Little was known about the boy caught in a bitter custody battle between his Singaporean father, 40, and Mongolian mother, 34.

Previous court papers would name the boy merely as M, and state that he was born in July 2012 and that he has been living with his father and paternal grandparents in Singapore since July 2013.

But more details emerged from the judgment yesterday, painting a profile of the five-year-old and his development amid the legal tussle.

Born in London and separated from his mother at the age of one, the boy was diagnosed with autism spectrum disorder (ASD) in March this year, on top of having a congenital lung condition.

ASD refers to a range of developmental disorders where individuals experience difficulty in socialising and communicating with others. It is estimated that one out of 150 children here has some form of ASD.

The boy is fond of numbers, according to the court papers. He was thrilled when playing mathematical games with his mother, who lives in England, through Skype. When playing a game of solving maths problem sums during the session, he would squeal with joy each time he had the right answer.

But he once said he felt "a little scared, sad and angry" when his father made him solve arithmetic puzzles that he did not like.

To M, his mother lives in a faraway land, and they may communicate only through electronic means.

Still, M delights in his mother's company despite being separated from her, said court documents.

He reacts quickly when interacting with his mother via Skype, and eases into engaging her through the computer screen. He takes the lead in conversations with her, initiating different topics, such as showing her pictures of the food that he likes.

He also picks up items from around the house to show her.

In contrast, he seldom approaches his father and grandmother at home, and does so only to make verbal requests with poor eye contact, according to a psychological report.

He is also inconsistent in responding to them when called by name, and might reply to questions or directions given to him only on his own terms, showing difficulty engaging in reciprocal conversations initiated by others.

In March last year, M met his mother in person for the first time in a long while, but still managed to recognise her immediately.

In May that year, when she came to Singapore again in hopes of taking him back to England, he approached her willingly when she was granted access to him.

The mother said they spent a "wonderful" day visiting a museum, a toy store and a play centre.