The estranged brother of the Singaporean prime minister has backed a new opposition party, the latest incident in a bitter feud in the city-state’s first family.

The Progress Singapore Party (PSP) was formed by Tan Cheng Bock, a former stalwart of the ruling party, to contest elections due by 2021.

Tan has been seen in recent months with the premier’s sibling, Lee Hsien Yang, local media reported, sparking talk of an alliance.

On Sunday Lee posted on Facebook: “I wholeheartedly support the principles and values of the Progress Singapore Party.”

“Today’s PAP is no longer the PAP of my father. It has lost its way,” he said.

He did not elaborate further or say whether he would join the new party.

Business executive Lee and his sister have been embroiled in a feud with their elder brother, Prime Minister Lee Hsien Loong, over the fate of a century-old family bungalow.

The rare public falling out within the city-state’s elite erupted following the 2015 death of their father, Singapore’s founding leader Lee Kuan Yew.

The PAP has governed Singapore for decades and the weak opposition is not viewed as a threat, but backing from a senior member of the Lee family could provide a boost to Tan.

A former PAP lawmaker, Tan resigned from the party in 2010 and unsuccessfully ran for president the following year. He will formally launch his party next week.

The prime minister, 67, has said he will lead the PAP at the next polls before handing power over to leader-in-waiting, Finance Minister Heng Swee Keat.

– Agence France-Presse