The eldest son of disgraced former President Chun Doo-hwan was questioned by prosecutors Friday as part of an ongoing probe into huge slush funds his father stashed away while in office in the 1980s, prosecutors said.

The senior Chun, then an army major general, seized power in a 1979 coup. In 1997, he was ordered by the Supreme Court to return to state coffers around 220 billion won (US$196.8 million) he illegally accumulated in bribes while in office from 1980-88.

Chun has yet to pay some 167.2 billion won he owes. Suspicions have grown recently that part of the slush funds might have been funneled into the businesses of his three sons.

In an unprecedented move, Chun Jae-kook, the former president's eldest son, announced on Tuesday the family's plan to voluntarily return to the state 170.3 billion won worth of real estate, movables and financial assets, an amount exceeding the unpaid money.

The Seoul Central District Prosecutors' Office tasked with reclaiming the unpaid fines said the younger Chun will be grilled over detailed methods of paying off the fines.

The younger Chun is also accused of setting up an overseas shell company and evading taxes in the process.

It marks the second time that a child of the former president has been called in for questioning in connection with the widening investigation.

Last week, the former president's second son, Chun Jae-yong, was also grilled by prosecutors over suspicions of evading large taxes in connection with a land deal in 2006. (Yonhap News)