Basma bent Saoud and her daughter Suhoud were detained in March 2019.
A Saudi princess detained without charge for nearly three years in Riyadh has been released, according to a human rights organisation.
"Basma bent Saoud and her daughter Suhoud, detained since March 2019, have been released," the London-based Saudi Arabia organisation ALQST said on Twitter.
"At no point during her detention has any charge been levelled against her," the NGO added, lamenting the "negligence" of the authorities in dealing with the princess's health condition.
Basma bent Saoud was arrested just before a trip to Switzerland for medical treatment, according to a source close to her family. The nature of her illness has never been disclosed.
The 57-year-old businesswoman and outspoken personality had appealed to King Salman and Crown Prince Mohammed bin Salman in April 2020 for her release on health grounds.
According to her family, Princess Basma, the youngest child of the late King Saud bin Abdul Aziz, was known for her stance in favour of reforms and her denunciation of abuses in Saudi Arabia.
The Saudi princess was detained in Al-Hair prison, located near Riyadh and known to host many political prisoners.
Once very discreet, the Saudi royal family has been vigorously shaken since the rise in 2017 of the crown prince nicknamed MBS, who has become the de-facto ruler of the rich oil monarchy.
Several prominent Saudi royals have been ousted or worried by the government. In March 2020, the royal guard arrested King Salman's brother and nephew on charges of plotting a coup against MBS, according to several sources.
NGOs regularly denounce the violations of rights and freedoms in this conservative kingdom and its attempts to soften its image around the world with sports events and pop music concerts.