A mistress killed the children she had with her long-time boyfriend the day after she discovered he had other lovers and children, the Court of First Instance heard yesterday. Lee Fung-yee, 38, served her 13-year-old son and 12-year-old daughter orange juice spiked with sleeping pills before burning charcoal in their home, the court heard. Lee has pleaded not guilty to two counts of murder over the deaths of the boy, Li Siu-hang, and girl, Li Po-ka, at their Tuen Mun flat on October 14 last year. She has said she will plead guilty to manslaughter. Prosecutor Graeme Hagon said the children died a day after Lee and boyfriend Li Kam-sze argued over his other lovers and children. Hours before the deaths were discovered, firefighters and police went to the flat because smoke was billowing from it, Hagon said. Lee turned them away by saying she was burning incense. Hagon described a complicated 'triangular relationship' between Lee, her boyfriend and his 61-year-old long-time girlfriend, Leung Wing-lan. Hagon said Lee met Li, the operator of a Buddhist hall in Tuen Mun where her mother often took her, in 1993 when he was living with Leung. They later developed a relationship and she became pregnant in 1994 at which time Leung, a divorcee, learned of her existence. They quarrelled over the relationship but Leung eventually agreed Lee could stay with Li and he housed her in one of more than 20 properties he owned in the building where he lived with Leung. Lee gave her first baby to Leung asking her to take care of him. After Lee gave birth to the younger pair, who lived with her, Li paid their expenses and gave her an allowance of HK$10,000 a month. Leung told the court the trio and the children had a harmonious life apart from some ups and downs. She had no children with Li but Lee's called her mother. Early on October 12 last year, Li and Lee argued over 'some girlfriends' the man had behind Lee's back. Leung recalled that Lee called at about 9pm that day saying: '[Li] has some children outside. How would he love my children?' The next day, at about 1pm, she received another call from Lee, who said: 'The two children had no response. I regained consciousness. I killed the children.' Leung asked her to report the matter to police if it was true. Lee said 'okay' and hung up. Leung said she then rushed back home, where she saw Li, who said he thought it was only a 'false alarm'. However, at 3pm, Leung and Li received a call from police saying Lee had had an accident. Leung will continue her evidence before Madam Justice Clare-Marie Beeson today.