The niece of Iran's Supreme Leader Ayatollah Ali Khamenei was arrested on Thursday after praising the wife of the former Shah.
Farideh Moradkhani, the daughter of Khamenei's sister, was on her way home in the Iranian capital Tehran when she was detained. Her arrest was later confirmed by her brother, Mahmoud, who lives in exile in France.
Moradkhani had participated in a virtual birthday celebration in October praising Farah Pahlavi, the widow of Mohammad Reza Pahlavi, Iran's monarch until he was ousted in the 1979 Iranian Revolution.
Shortly after the autocrat's overthrow, the country transitioned to theocratic rule.
Farah Pahlavi is also based in France.
Khamenei's niece allegedly addressed Farah Pahlavi as "dear queen" and called on her to return to Iran.
After Moradkhani was detained, security forces reportedly searched her home and confiscated belongings, according to Human Rights Activists News Agency [HRANA]. Moradkhani is reportedly being held in the notorious Evin prison in Tehran.
Monarchism is illegal in Iran, and supporters of the former shah can face imprisonment.