Ousted South Korean President Park Geun-Hye is being questioned by prosecutors over a corruption scandal that brought her down.
After arriving at the office, she told reporters she was “sorry”, adding: “I will undergo the investigation sincerely.”
Prosecutors are expected to hold Ms Park for a marathon questioning session that will last till late in the night.
On Tuesday, Ms Park’s supporters gathered outside her home in an affluent suburb of Seoul, as she was escorted by police to the prosecutors’ office in a short journey covered live on television.
Her dismissal was confirmed by the country’s top court earlier this month, ending the political career of a woman who grew up in the presidential palace as the daughter of army-backed dictator Park Chung-Hee.
An election will now be held by 9 May.
Hwang Kyo-Ahn, who is loyal to Ms Park, is currently the acting president.