Born around 1939 in Singapore, Wong Weng Siu, later known publicly as Mimi Wong, was the daughter of her father's second wife. Her life from the very beginning was marked by hardship. Wong's father died before she turned one, and her mother, struggling financially, left her in the care of her father’s first wife and nine half-siblings. This arrangement proved traumatic — Wong endured constant verbal and physical abuse from her guardians, and she was treated like an outsider in her own family.

Denied an education, Wong began working at just 14 years old to support herself. She took on a job in a factory, but the weight of extreme poverty never left her. At 17, she met Sim Woh Kum, a sweeper and school canteen stallholder. After dating for two years, they married in 1958 and had two sons, born in 1958 and 1962 respectively.

The marriage was turbulent. Wong, known for her fierce temper, frequently physically assaulted Sim, sometimes with weapons. Sim endured the abuse in silence, often fleeing their home during violent episodes. At the same time, Sim was a compulsive gambler, frequently losing their money and eventually his job. To support the family, Wong worked part-time jobs, eventually becoming a bar hostess under the name Mimi Wong.

By 1963, the relationship had unraveled. Wong left Sim, and he was left to care for their children and elderly mother alone. Wong, meanwhile, leaned into her new identity in the nightlife world. With her looks and confidence, she became one of Singapore’s most sought-after cabaret girls — “queen of all hostesses.”

In 1966, she began an affair with Hiroshi Watanabe, a Japanese engineer working in Singapore. Despite knowing he had a family in Japan, Wong became his mistress. Their relationship was rocky and eventually ended, but not before Wong aborted one of his children and later gave birth to another child with a different man.

Still, Watanabe continued supporting Wong and her daughter financially. She lived in a rented house with a servant, funded by Watanabe, who gave her $200 a month. In 1969, Watanabe confessed the affair to his wife, Ayako Watanabe, who flew to Singapore with their children.

On January 6, 1970, Mimi Wong and her ex-husband Sim Woh Kum entered the Watanabe family’s rented home at Jalan Sea View under the pretense of fixing a toilet. Wong had been enraged after hearing from Hiroshi that his wife allegedly called her a “prostitute.” Fueled by jealousy and emotional instability, she planned Ayako's murder and convinced Sim to help — offering him money and playing on his lingering affection for her.

Once inside the house, Sim splashed toilet-cleaning liquid into Ayako's eyes while restraining her. Wong then stabbed Ayako multiple times in the neck and abdomen. The gruesome attack was witnessed by nine-year-old Chieko Watanabe, Ayako’s daughter, who later testified in court. Ayako staggered out of the bathroom before dying in front of her children.

Wong and Sim fled. She hid with her amah and reportedly confessed to stabbing a Japanese woman while drunk. Police arrested both the next day. Chieko identified them in a lineup, and both were charged with murder.

Their 26-day trial began in November 1970, prosecuted by Francis Seow. Wong pleaded diminished responsibility, claiming she had a brain infection and was mentally impaired. Sim said he tried to break up the fight and was bitten in the process. Both accused each other of being the mastermind.

The judges rejected their defenses. On December 7, 1970, both were convicted and sentenced to death — making them the first couple in post-independence Singapore to receive capital punishment.

Appeals followed. In 1972, renowned lawyer David Saul Marshall argued on Wong's behalf, citing humanitarian reasons and mental instability. The appeals were denied. A clemency petition to President Benjamin Sheares was also rejected on July 23, 1973.

Wong spent three years on death row in Changi Prison. She was a difficult inmate, reportedly throwing urine and stripping naked in her cell. The only person who could calm her was Darshan Singh, the prison's chief executioner, with whom she formed a strange bond. She converted to Christianity and began reading the Bible.

On July 27, 1973, Mimi Wong, aged 34, and Sim Woh Kum, 40, were hanged at dawn. Wong wore her wedding dress to the gallows. Before dying, she told Singh she wanted to be his lover in the next life and "take him with her." Singh became gravely ill after her execution.

Wong and Sim were buried side by side. Her four-year-old daughter left flowers and a note that read: “To my beloved mother.”