Stella Obasanjo, wife of Nigeria's President Olusegun Obasanjo, died after cosmetic surgery, a doctor has said.
Stella Obasanjo was considered Olusegun's official wife
Mrs Obasanjo died on Sunday in Spain, where she had gone for the operation.
Results of an autopsy performed in the town of Malaga on Monday not been made public but have been given to a judge investigating the death.
Mrs Obasanjo, 59, was a controversial figure who ordered the arrest of a newspaper publisher earlier this year over an article headed "Greedy Stella".
The autopsy lasted two-and-a-half hours and seems to have given clear information on the cause of death, Antonio Garcia de Galvez, director of the Malaga Institute of Forensic Medicine, told the Associated Press news agency.
He did not give further details on the cosmetic procedure that the first lady was undergoing.
In a television broadcast announcing Mrs Obasanjo's death, presidential spokeswoman Remi Oyo said books of condolence had been opened at the Banquet Hall of the State House in Abuja, the State House Marina in Lagos, and at the president's home in Otta.
Olusegun Obasanjo had several wives before returning to power in 1999, but since he became president Stella had been considered his official wife, the AFP news agency reports.
Newspaper publisher Orobosa Omo-Ojo was detained earlier this year after his newspaper, the Midwest Herald, ran an article entitled "Greedy Stella".