The grandson of the founder of OG department store was fined $3,500 yesterday for harassing the husband of his then alleged lover.

Kelvin Liu Chin Chan was found guilty of one charge under the Protection from Harassment Act, brought by the woman's husband, civil servant Desmond Tay Kwang Ju.

Liu, 44, committed the offence between June 2016 and January 2017 while married to another woman.

On July 6 last year, during the trial, Mr Tay said Liu had harassed him with text messages and photographs intended to belittle him and cause him distress.

In his testimony, Mr Tay, who turns 40 this year and is attached to the Singapore Consulate General in Shanghai, said he learnt of the alleged affair when Liu's then wife contacted him in May 2016.

She alleged that his then wife, identified only as Madam Lin, was planning a trip to Hong Kong with Liu the following month.

Mr Tay revealed that after being told of the alleged affair, he hired a private investigator and found out that his wife and Liu had travelled to Hong Kong from June 7 to 10 that year. However, Madam Lin later denied that she was cheating. To clarify the issue, she got her husband to create a chat group with all four parties included.

But in the group, which he named "Confessions of Marco Polo", Liu sent belittling and humiliating messages, calling Mr Tay an "idiot" and a "wayang king". Liu also asserted that Mr Tay was lying about the nature of Madam Lin's alleged affair.

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

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 was superior to me in physique, which is why my wife is with him and not me."

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.

During the trial, Liu claimed Mr Tay had made several threats to him through third parties. He also produced WhatsApp conversations in court in which Mr Tay called him "a real joke" and said he was prepared to tell everyone about the case.

The Straits Times understands that Liu is now married to Madam Lin.

The case has been adjourned to Aug 13 for a hearing on the issue of costs. Liu belongs to one of Singapore's richest families. His grandfather was the late billionaire Tay Tee Peng, and their family made the Forbes list of wealthy individuals.