His family did not think he would get married. But at the age of 72, when he was critically ill in Taiwan and just 18 days from his death, Mr Pua Ching Kiong mysteriously wed a Taiwanese woman on Feb 24 last year.

On Tuesday, the mystery took on a darker shade when his wife Huang Kuan-chen, 55, was detained in Taiwan and is under investigation for suspected fraud, reported Focus Taiwan News.

Her alleged accomplice Liu Wen-pin, 63, was also arrested.

Huang had married Mr Pua primarily to get at his NT$100 million (S$4.2 million) fortune, Taiwanese media reports said, quoting Taiwan's Criminal Investigation Bureau.

His family members said he was coerced into the marriage.

Mr Pua was the owner of Pua Loong Trading Company, which sells Dragon Balm, a liniment for aches and pains.

He first met Huang at a religious event 30 years ago but they were only acquaintances back then. The two met again in 2014.

Mr Pua travelled to Taiwan in December that year, when an old friend invited him over to treat his diabetes, said his younger sister, who wished to be identified only as Madam Pua. She now manages the company.

Mr Pua was supposed to return to Singapore on Dec 25 but got hospitalised for 42 days instead.

The family met Huang for the first time in January last year. Mr Pua had a fall the following month and was not able to talk.

"It was very hard to communicate with him, because he was hard of hearing and blind in one eye. Through the phone it's worse, so we always communicated with Huang after my brother fell," she said.

Huang claimed more than NT$1 million from Mr Pua's family in Singapore, for his "medical bills".

On Feb 24 last year, Mr Pua sought emergency treatment at the hospital and was later taken to register his marriage with Huang, while he was in a wheelchair.

Mr Pua's nurse later admitted to the police that Huang guided Mr Pua's right hand as he signed the certificate.

She also said that Huang and Liu were a couple.

Madam Pua said her brother had not planned to marry.

The family rushed to Taiwan after he was hospitalised on March 2 last year. Days after his death on March 13, he was cremated.

But when the family members were given the medical receipts by senior staff from Mr Pua's company, they found discrepancies in the documents and suspected something was amiss.

They contacted the hospitals involved and their suspicions were confirmed. "We found the writing on the marriage certificate was very similar to Huang's, and suspected that it was not written by my brother. He usually didn't sign his name like that," said Madam Pua.

After Mr Pua died, Huang, as his widow, tried to lay claim to his assets. The family, in turn, filed a case against Huang in May last year and are waiting for the marriage to be annulled.

Madam Pua said Huang had projected "an angel's image".