She was carrying her lover's child and wanted to get hitched.
But Ms Zhao Dan, 30, did not know her lover Ong Tiong San, 43, was married with children, and would not be able to register their union.
To get around this, Ong paid someone $120 to stage a solemnisation ceremony at his home, and created a fake marriage certificate by modifying a scanned copy of his real one.
He repeated the trick after Ms Zhao gave birth to a girl in February this year, this time using his son's birth certificate as the template for a bogus one.
Ms Zhao, a Chinese national, remained none the wiser. But the deception finally fell apart when the retail supervisor returned to work in May, and submitted the false documents to claim maternity leave benefits from her employer.
Yesterday, Ong was fined $10,000 after pleading guilty to two counts of forgery.
It is understood the couple met while working at NTUC FairPrice, where he was a division manager. Ong stopped working for FairPrice in August.
The court heard that on Jan 25, he used PowerPoint software to produce the bogus marriage certificate. This stated that his purported union with Ms Zhao had been solemnised by an assistant registrar of marriages.
Sometime between late February and early March, he made the fake birth certificate, which said their newborn girl was a Singapore citizen.
Ong later paid NTUC FairPrice $4,067.30, for the 48 days of maternity leave benefits Ms Zhao was not eligible for, after his forgeries were discovered.
Ong also admitted making a false statement in March at the Immigration and Checkpoints Authority. In a form to register their child's birth, he stated the couple had been married in Singapore on Jan 25.
Calling for the $10,000 fine, Deputy Public Prosecutor Eunice Lim said the documents forged were of a serious nature.
District Judge Carrie Chan said the offences were "shocking", noting Ong's previous convictions in 1992 and 1999 - for criminal breach of trust and cheating - both involved dishonesty.
She said Ong had planned the forgeries and deceived his lover for a long time.
The judge noted that besides a fine, forgery carries a maximum jail term of four years. She warned Ong that imprisonment was likely if he were to reoffend.
Pleading for leniency, Ong told the court he now needs to support three children, two of whom are from his existing marriage. He later told reporters it would take about two months to complete divorce proceedings for this. Ong and Ms Zhao would wed after that.
When asked if she forgave him for the lies, Ms Zhao, who had accompanied Ong to court, smiled. She said in Mandarin: "What else can I do?"