This is for the first time Tharoor has been questioned on death of 52-year-old Sunanda. She was found dead at a luxury hotel on January 17 last year.
The former union minister has been questioned by the Special Investigation team led by Additional DCP (South) PS Kushwah.
Tharoor reached the office of Anti Auto Theft Squad (AATS) in South Delhi at around 8 PM where he was questioned by a five-member SIT team. Tharoor was issued a notice by SIT to join investigation.
Sources said Tharoor will be questioned about the happenings of January 17, 2014 when Sunanda was found dead.
He would also be questioned about the circumstances in which Sunanda had left him at the airport after returning from Thiruvananthapuram to Delhi on January 15 and checked in at Leela Hotel.
Specific questions will also be asked about the reported tiff he had with Sunanda over his alleged affair with Pakistani journalist Mehr Tarar.