Mr Lee Hsien Yang, who has been embroiled in a public feud with his brother, Prime Minister Lee Hsien Loong over their late father's house at 38, Oxley Road, was spotted in Hong Kong on Sunday (June 25) after taking a flight from Singapore.
Hong Kong media reported that Mr Lee Hsien Yang was accompanied by his wife, Mrs Lee Suet Fern, and that no one was at the airport to receive them.
He told Hong Kong media he was in the city to visit friends, and declined to comment on his dispute with PM Lee.
Mr Lee and his sister, Dr Lee Wei Ling, took their dispute with PM Lee into the public sphere on June 14, when they issued a statement accusing their older brother of misusing his power to drive his personal agenda.
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Mr Lee Hsien Yang and his wife had also said they were preparing to leave Singapore, but did not disclose where they intend to live.
It is unclear if Mr Lee is planning to relocate to Hong Kong. When asked by Hong Kong media when he was leaving Hong Kong, he replied: "That has nothing to do with you."
The dispute that Mr Lee and his sister made public centres on whether to demolish former prime minister Lee Kuan Yew's Oxley Road house.
Other points of contention include the contents of the late Mr Lee's final will and the circumstances in which it was prepared.
The siblings said they feared the use of organs of state against them, to the extent that Mr Lee Hsien Yang felt compelled to leave Singapore "for the forseeable future".
Global law firm Morgan Lewis & Bockius has said that Mrs Lee Suet Fern, the managing partner of its combined practice in Singapore, has stepped down from that role.
But a spokesman from the firm had earlier said Mrs Lee will continue to play a key role in its global strategy from offices in Singapore and in Hong Kong.
She added that Mrs Lee will "continue to spend a significant amount of time in Singapore as well as travel to Hong Kong, as she already does... ".
Mr Lee Hsien Yang and his sister Dr Lee have made multiple Facebook posts criticising PM Lee, his wife Ho Ching, and a ministerial committee chaired by Deputy Prime Minister Teo Chee Hean to consider options for the Oxley Road house.
In a Facebook post on Sunday night, Dr Lee said PM Lee had admitted in public for years that the late Mr Lee was "unwavering" in his wish to demolish the house, but "now he and his ministers tell us that Lee Kuan Yew changed his mind".
"The people of Singapore will see through LHL's attempt to rewrite the past," she wrote.
On July 3, PM Lee will deliver a ministerial statement in Parliament in response to the allegations.