The grandson of one of Singapore's richest families is in court for harassing his alleged lover's husband.

Kelvin Liu Chin Chan, 43, who was married then, faces one charge under the Protection from Harassment Act brought by civil servant Desmond Tay.

Liu's grandfather is the late billionaire Tay Tee Peng, the foun-der of OG department store. The family has made the Forbes list for its wealth.

Mr Desmond Tay, who is currently attached to the Singapore Consulate-General in Shanghai, took the stand yesterday to accuse Liu of harassing him with text messages and photographs intended to belittle and cause distress to him.

In his testimony, Mr Tay, 39, said he learnt of the alleged affair only when Liu's wife contacted him on May 31, 2016.

She alleged that her husband and Mr Tay's wife, a Madam Lim, were having improper relations.

He was also told that his wife and Liu were planning a trip to Hong Kong together in June that year.

Mr Tay revealed that after being told about the alleged affair, he hired a private investigator and found out his wife and Liu travelled to Hong Kong from June 7 to 10 that year.

Later that month, Madam Lim denied she was cheating on Mr Tay.

To clarify the issue, she told Mr Tay to create a WhatsApp chat group with all four parties included. He did so and named it "Confessions of Marco Polo".

But in the chat group, Liu allegedly sent belittling and humiliating messages, calling Mr Tay an "idiot" and "wayang king", and asserted that Mr Tay was lying about the nature of Madam Lim's relationship with Liu.

Mr Tay testified that he also felt that Liu was being condescending to him by calling him "Des" because the two men were unacquainted with each other.

He added that he felt mocked over his lack of wealth and knowledge when Liu questioned him about the legal requirements for adultery and told him to seek advice from lawyers working for prominent firms.

Mr Tay said Liu sent him two photos - a topless picture of Mr Tay, which was taken by Madam Lim in private, and a photo of a topless torso with the face obscured, believed by Mr Tay to be Liu himself.

Mr Tay said: "I think he wanted to let me know that he had something private of me and make me feel vulnerable.

"It felt like he was trying to say he is superior to me in physique, which is why my wife is with him and not me," he added.

It was heard in court that Mr Tay's wife filed for divorce in August 2016. But he filed a defence and counterclaim on the basis of adultery.

Liu, who is representing himself, yesterday cross-examined Mr Tay, claiming the younger man had made several threats to him through third parties. He produced WhatsApp conversations in court where Mr Tay called him "a real joke" and said he was prepared to tell everyone about the case.

Madam Lim and her mother Madam Tan will be taking the stand as witnesses for Liu.

The case has been adjourned for a pre-trial conference.

For harassment, Liu can be jailed for up to a year and liable to a $10,000 fine.