Singapore Prime Minister Lee Hsien Loong's younger brother and his wife are on the run after they came under investigation for lying during judicial proceedings related to the will of their late father, Lee Kuan Yew, the founding and first leader of the city-state, Parliament was told on Monday.

Lee Hsien Yang and his lawyer wife, Lee Suet Fern, were found to have lied under oath in 2020 by the Court of Three Judges and a disciplinary tribunal police investigation over the latter's handling of the last will of founding Prime Minister Lee, who died on March 23, 2015, at the age of 91.

Home Affairs and Law Minister K. Shanmugam told Parliament that police named the duo and released information about the case in the public interest.

The disclosure did not cause any material prejudice to the couple as their conduct was already a matter of public record, given that a disciplinary tribunal and a court found that the duo had lied.

Responding to questions, Mr Shanmugam said that while the general principle is that law enforcement agencies do not disclose the names of people under probe, in a wide variety of situations, it may be necessary to do so.

Police typically disclosed names in situations where those being investigated have evaded authorities, the minister said. He added that in case public interest is involved in the investigation or if the people and facts of the offences under probe are already publicly known, police make investigations public.

The circumstances relating to Lee and his lawyer wife straddle these two examples, Mr Shanmugam said, adding that the couple absconded after the police contacted them to assist in investigations.

The findings of the tribunal and the court - that the couple was not telling the truth and were dishonest - are also already matters of public record, and thus, disclosing the police investigation in Parliament will not "materially add to any cloud the couple may already be under", the Straits Times newspaper quoted Mr Shanmugam as saying.

The couple left Singapore after refusing to go for a police interview that they had initially agreed to attend, Senior Minister Teo Chee Hean told Parliament earlier this month.

Police later said they left Singapore after being engaged in June 2022 and have not returned since.

Fern, 64, had been referred to a disciplinary tribunal by the Law Society over her role in the preparation and execution of the last will of the city-state's founding Prime Minister, which differed from his sixth and penultimate will in significant ways. It did not contain some changes Lee had wanted and discussed with his lawyer, Kwa Kim Li, a few days earlier.

Among the differences was a demolition clause - relating to the demolition of Lee's 38 Oxley Road house after his death - which had not been in the sixth or penultimate will but was in the last.

This clause became a sticking point among the late Lee's children.

Fern's role in the will had sparked a complaint by the Attorney-General's Chambers to the Law Society about possible professional misconduct on her part.

After the disciplinary tribunal found her guilty of grossly improper professional conduct, it referred the case to the Court of Three Judges, the highest disciplinary body to deal with lawyers' misconduct.

Fern was suspended by the Court of Three Judges from practising as a lawyer for 15 months, according to The Straits Times newspaper.