Samsung's heir apparent Lee Jae-yong has been placed under arrest in South Korea, accused of bribery and other charges.
According to media reports, the case is linked to a scandal that led to the impeachment of the country's President Park Geung-hye.
Lee is currently vice-chairman of Samsung Electronics. But since his father, Lee Kun-hee, suffered a heart attack in 2014, he is considered de facto boss of the entire Samsung Group conglomerate.
Samsung is accused of giving donations to non-profit foundations operated by Choi Soon-sil, a friend of Park, in exchange for government favours. Lee and the Samsung Group denied any wrongdoing.
"We will do our best to ensure that the truth is revealed in future court proceedings," the Samsung Group said in a brief statement following Lee's arrest.
The Samsung chief had already been questioned with several other company executives in January but a subsequent court ruling decided there was insufficient grounds for an arrest.
But on Friday, a court spokesman said in a statement: "It is acknowledged that it is necessary to arrest (Lee Jae-Yong) in light of a newly added criminal charge and new evidence."
Lee has been in detention since he was summoned back to court for a hearing held behind closed doors earlier this week.
Prosecutors accused Lee of giving bribes worth 41 billion won (USD 36 million) to President Park and her close friend Choi Soon-sil to win government support for a smooth leadership transition within Samsung.
Lee Jae-yong, also known as Jay Y Lee, first gave evidence in front of a parliamentary hearing in December last year. Since January he has been treated as an official suspect in the case.
At the parliamentary hearing, Samsung admitted giving a total of 20.4 billion won to two foundations, but denied seeking favours in return.
And Lee also confirmed the firm gave a horse and money to help the equestrian career of Choi's daughter, Chung Yoo-ra, something he said he now regretted.
Prosecutors now have 20 days to detain and question him before they have to formally indict Lee.