Ashraf Pahlavi, the twin sister of Iran’s late shah who vigorously defended the toppled, American-backed monarchy and whose life was marked by intrigue, privilege and personal tragedy, died Jan. 7 at 96.

Reza Pahlavi, a son of the shah, announced the death on his official Facebook page. The cause was not immediately disclosed. Iranian state television said she died in Monte Carlo.

Ms. Pahlavi was one of the last surviving siblings of the shah, whose family reigned from 1925 until the Islamic revolution in 1979.

In a life that spanned continents and conflicts, Ms. Pahlavi encompassed the full sweep of the Pahlavi dynasty. Her mix of glamour, lavish living and misfortune attracted the attention of feature writers and society pa­ges. Pop artist Andy Warhol embellished her image with jet-black hair and candy-red lips.

She also drew the admiration of Soviet leader Joseph Stalin, who once told her to carry a message back to her brother: “If he had 10 like you, he would have no worries at all.”

Princess Ashraf Pahlavi of Iran talks with Secretary-General Kurt Waldheim of the United Nations in 1975. (Vcm/AP)

Ms. Pahlavi was raised in the gilded but cloistered world of a princess after her father, Reza Pahlavi, seized control from the fading Qajar dynasty, then watched Allied powers in World War II push him into exile in favor of her brother.

She rode the new era to a position as palace adviser, including playing a key role in opening doors for an American-engineered coup in 1953 to protect the monarchy. From exile after the revolution, she lived in regal splendor in New York and Paris but also was touched by heartbreak that included the fatal shooting of one of her three children in 1979; she claimed it was a politically motivated slaying by fanatics associated with the ­revolution.

From a young age, Ms. Pahlavi carved out an outsize reputation defined by bold gestures and her sharp tongue. She and her sister, Shams, were among the first prominent Iranian women in the early 1930s to appear publicly without Islamic head coverings.

During the height of her brother’s rule — flush with oil revenue — she adopted a jet-set lifestyle with homes in New York, Paris and the French Riviera, where she was a high roller in its casinos.

She developed a role as a champion for women’s rights. In 1967, she was Iran’s delegate to U.N. groups, including the Commission on Human Rights. She addressed the United Nations in 1975 for International Women’s Year.

Some critics questioned her credibility because of her lack of direct activism and how female dissidents were among those persecuted and jailed by the Iranian monarchy.

She viewed herself as someone who had symbolized the emancipation of Iranian women and was appalled, after returning from a trip to the Soviet Union in 1978, at seeing many of her sex donning “the mournful black chador their grandmothers had worn,” she told British author William Shawcross for his book “The Shah’s Last Ride.”

“My God, I thought, is this how it ends?” she added. “To me it was like seeing a child you had nurtured suddenly sicken and die.”

After the shah’s death in Egypt in 1980 from cancer, Ms. Pahlavi was outspoken about enemies real and perceived. Besides Ayatollah Ruhollah Khomeini and his followers who led the Islamic revolution, her list of foes included President Jimmy Carter, who she said “abandoned” her brother for political reasons.

Ms. Pahlavi lashed out at detractors who alleged that the monarchy had siphoned off a fortune for its own use. She claimed that she and others had legitimate revenue from inherited property and businesses but generally sidestepped complaints that the land was expropriated and that key enterprises were all overseen by the shah and his royal court.

She was a prominent apologist for the shah’s notorious secret police, known as Savak, which led relentless crackdowns on dissidents and was accused of widespread abuses.

From exile in Paris, she embraced the nickname “la Panthère Noire,” or the Black Panther, bestowed by a French journalist. “I must admit that I rather like this name, and that in some respects it suits me. Like the panther, my nature is turbulent, rebellious, self-confident,” she told the New York Times in 1980.

“Often, it is only through strenuous effort that I maintain my reserve and my composure in public,” she continued. “But, in truth, I sometimes wish I were armed with the panther’s claws so that I might attack the enemies of my country.”

Ashraf Pahlavi was born in Tehran on Oct. 26, 1919, five hours after her twin brother — children of a military commander, Reza Pahlavi, and the second of his four wives. Their father would soon become the country’s power broker after leading troops that drove invading Soviet forces out of Tehran.

It was the last gasps of the Qajar dynasty, which had ruled Persia since the late 18th century. Reza Pahlavi gradually consolidated control until the collapse of Qajar rule in 1925 and his own rise as the new shah.

He began Western-inspired reforms and cultural pivots such as opposing mandatory Islamic coverings for women. He formally changed the country’s name from Persia to Iran, which reflects the belief in an ancient heritage linked to Aryan tribes in present-day Russia.

Ms. Pahlavi’s twin brother, Mohammad Reza Pahlavi, received lavish attention as the crown prince amid 10 other brothers, sisters and half siblings. Ms. Pahlavi complained about being denied a university education and forced into a marriage in 1937 to Mirza Khan Ghavam, a member of a prominent Iranian family that was an important ally of the shah.

They divorced after five years: the first of three complicated — and apparently unhappy — attempts at marriage.

Meanwhile, the royal court was moving toward upheaval. In 1941, the first shah was pushed into exile by Allied powers in World War II because of fears about his pro-German sympathies. Ms. Pahlavi’s brother took the throne.

This ushered in a period of special influence for Ms. Pahlavi as one of her brother’s closest advisers, including being sent as an envoy in 1946 to meet with Stalin to discuss the Soviet hold over neighboring Azerbaijan, which shares ethnic bonds with many Iranians.

Her real clout was highlighted in 1953 during a power struggle between the shah and Iran’s elected prime minister, Mohammad Mossadegh, who sought to nationalize Iran’s oil industry and limit the shah’s sweeping author­ity.

The shah was initially reluctant to accept an American-led plan to attempt a coup to oust Mossadegh. But Ms. Pahlavi was courted by U.S. and British agents, including one who reportedly brought gifts of cash and a mink coat. Many historians say she eventually helped sway the shah to support the coup, which toppled Mossadegh and ushered in decades of increasingly authoritarian rule by the monarchy.

Ms. Pahlavi ended her marriage with her second husband — a well-connected Egyptian, Ahmed Shafiq Bey — and in 1960 wed an Iranian emigrant in France, Mehdi Bushehri, who ran an Iranian cultural center in Paris. Ms. Pahlavi, however, spent most of her time at her New York townhouse on Beekman Place, and the couple maintained largely separate lives.

A son from her second marriage, Shahriar Shafiq, an imperial navy captain, was killed by a gunman in Paris in 1979; a member of the Islamic government asserted responsibility for the death. A daughter from her second marriage, Azadeh Shafiq, died of leukemia in 2011.

A list of survivors was not immediately available.

Ms. Pahlavi defended her family’s reputation in her 1980 ­memoir, “Faces in a Mirror,” and later in books such as the French-language “Jamais Résignée” (“Never Resigned”) and “Time for Truth,” the latter written with Tomi Keithlen.

She gradually retreated from public life. She spent most of her time in her guarded Right Bank apartment in Paris, playing bridge with friends and watching movies and old footage from pre-revolution Iran.

“At night, when I go into my room,” she told the Associated Press in 1983, “that’s when all the thoughts come flooding in. I stay up until 5 or 6 in the morning. I read, I watch a cassette, I try not to think. But the memories won’t leave you.”

In 2014, Iran’s Fars News Agency published a rare photo of Ms. Pahlavi in public. Fars identified her with Ardeshir Zahedi, the former shah-era ambassador to the United States and onetime companion to actress Elizabeth Taylor.