Singapore’s ruling People’s Action Party was rocked by two unexpected resignations, including that of parliament speaker Tan Chuan-Jin, further fueling one of the biggest political crises in the city-state’s history.

Once seen as a potential prime ministerial candidate by political observers, Tan, 54, stepped down from positions in government and the party, Prime Minister Lee Hsien Loong said in a statement Monday. He is the second Parliament speaker to resign for having an inappropriate relationship in just over a decade.

His resignation is the latest in a series of scandals to send shockwaves through Singapore, including a graft probe against a cabinet minister and investigations into pricey rentals by two other members of Lee’s administration. This comes at a precarious time for the PAP, which is navigating a leadership succession in its nearly six decades of power and battling voter unhappiness over rising living costs.