SINGAPORE - The niece of a wealthy 87-year-old widow has started legal proceedings against Madam Weng Yandan, wife of former China tour guide Yang Yin.

"My lawyers have today, among other things, filed further applications in the High Court suit to include Mr Yang Yin's wife as a second defendant and to extend the worldwide Mareva injunction to include her assets," said Madam Hedy Mok, 60, in a press statement on Friday evening.

This is the latest twist in the legal tussle involving Mr Yang and Madam Mok over control of the assets of widow Madam Chung Khin Chun. The assets are estimated to be worth $40 million.

The 40-year-old Yang met Madam Chung in 2008 while he acted as her private tour guide during a holiday in Beijing. A year later he came to stay with her in her Gerald Crescent bungalow. His wife and children now aged two and eight, came to stay with Madam Chung in 2013. But last month, Madam Mok accused him of manipulating her aunt and started legal proceedings.