Ling Jihua: China investigates top aide to former president
China has launched an investigation into former President Hu Jintao's most senior aide, state media report.
Ling Jihua is accused of "disciplinary violations", Xinhua news agency said, which usually refers to corruption.
He was demoted in 2012 after reports that his son had died crashing his Ferrari sports car in Beijing.
Correspondents say the investigation shows current President Xi Jinping feels secure enough to detain even the trusted advisers of his predecessor.
Xi Jinping took over from Hu Jintao as the Communist Party leader and China's president in late 2012.
Since the transition, Mr Xi has introduced a wide-ranging crackdown on corruption, warning it could threaten the party's very survival.
The BBC's Martin Patience in Beijing says the case again highlights that China's anti-corruption campaign has real teeth and that no-one - no matter how senior - is untouchable.
Analysis: Carrie Gracie, BBC News China editor
President Xi Jinping has described his anti-corruption campaign as a fight against tigers as well as flies.
This year has seen a succession of once untouchable Communist Party officials making tearful confessions in courtrooms before shuffling off to serve long prison terms.
But even by the sensational standards of recent months, Ling Jihua is a very big tiger indeed.
He was, in effect, presidential chief of staff to Mr Xi's predecessor, Hu Jintao - the gatekeeper at the very heart of power for a decade.
Ling Jihua's problems began more than two years ago when rumours began to swirl about an alleged cover-up over his son, who died while driving his Ferrari alongside two semi-clad young women.
Over recent months the net has been closing in on the entire Ling family as corruption investigations were announced into one brother after another.
But Monday's announcement about Ling Jihua brings the anti-corruption campaign very close to a former president - an unmistakable message to the public that the entire system is riddled with corruption.
Moreover, after two years and thousands of arrests, the campaign to eradicate this corruption is by no means over.
Earlier this month it was announced that former Chinese security chief Zhou Yongkang was facing corruption charges - a move that sent shockwaves through the political elite.
A week later, former top economic official Liu Tienan was jailed for life for accepting millions of dollars in bribes.
Critics say President Xi's campaign is as much about eliminating political rivals as it is about tackling corruption.
But by taking on such senior officials, President Xi will win the support of the public, our correspondent adds.
Until the scandal involving his son, Mr Ling had been tipped for promotion to the party's Politburo.
Instead, he was moved from head of the Central Committee's General Office - in effect chief of staff to China's leader - and appointed to the less influential post of head of the United Front Work Department.
The identity of those inside the Ferrari was never revealed and censors blocked online comments mentioning the crash.
However, reports said Mr Ling's son was behind the wheel and the two passengers were described as scantily-clad women. Mr Ling was accused of trying to cover up the scandal.