Maria Callas' real-life relationship with Aristotle Onassis was rocky until his death

• Opera singer Maria Callas' real-life relationships are depicted in the new Netflix biopic "Maria."
• Callas had a longtime affair with Greek shipping tycoon Aristotle Onassis.
• They continued seeing each other even after Onassis married Jackie Kennedy.

Famed singer Maria Callas gets the Hollywood biopic treatment in Pablo Larraín's new film "Maria," which stars Angelina Jolie as the opera legend.

The movie chronicles the last days of the soprano's life as she tries to find her singing voice again, which earned her the nickname "La Divina." Callas died of a heart attack in her Paris home on September 16, 1977, at the age of 53.

"Maria" also includes flashbacks of Callas' glory days as a performer and her relationships with her husband and manager Giovanni Battista Meneghini and her lover Aristotle Onassis.

Onassis, a Greek shipping magnate, had a well-known affair with Callas during his marriages to Athina Maria "Tina" Livanos and Jackie Kennedy. "Maria" implies that Callas was Onassis' true love.

Here's what to know about Callas' relationships with the shipping tycoon.

The real Maria Callas met Aristotle Onassis during her marriage to Giovanni Battista Meneghini

Callas and Meneghini were married from 1949 to 1959. They met in Italy in 1947, when she was a 23-year-old rising opera singer and he was a 51-year-old brick manufacturer.

In "Maria," Callas meets Onassis at a lavish party and he wastes no time professing his love for her, despite both of them being married to other people.

"I'm ugly, but I'm rich. I'm Greek, but I'm from Argentina. I'm married, but it's 1959," he tells Callas.

In real life, Callas met Onassis at a party in 1957 and he courted her while she was married to Meneghini.

Callas and Onassis attended various social events together during their romance, including then-president John F. Kennedy's 1962 birthday party. Marilyn Monroe, who was rumored to be having an affair with Kennedy, famously sang a sultry rendition of "Happy Birthday" to the president at the event. Callas also performed at the Democratic fundraising dinner at Madison Square Garden and was photographed chatting with him at a reception.

After Callas ended her marriage to Meneghini, she continued dating Onassis. In interviews, Callas said that Onassis didn't want her to sing.

Lyndsy Spence, the author of the biography '"Cast a Diva: The Hidden Life of Maria Callas," said that Callas had two miscarriages during her relationship with Onassis, in 1960 and 1963. Spence said that Callas became pregnant with Onassis' child again in 1966 and likely had an abortion.

A diary of one of Callas' close friends, which Spence was given access to for the biography, said that Onassis drugged the singer "mostly for sexual reasons."

Despite their yearslong relationship, Callas and Onassis never married.

In a 1974 interview with Barbara Walters, Callas said that after getting married and divorced, she was "frightened" of getting married again. She also said that she didn't believe in marriage.

"I think love is so much better when you're not married," she said.

Callas and Onassis' relationship continued during his marriage to Jackie Kennedy

Jackie Kennedy isn't a character in "Maria," but she is referenced in the film. In a flashback, a sickly Onassis tells Callas that he loves her, but he still hates the opera. Callas gets emotional and says that her pride, not her heart, was hurt when she found out via the newspaper that he married Kennedy.

Onassis tells Callas that he always loved her, and then the singer exits via the back door so Kennedy doesn't see her.

"Even in death, I was the secret," Callas recalls.

In real life, Onassis and Kennedy married on Onassis' private Greek island Skorpios in 1968 and remained married until Onassis' death in 1975. During that time, Onassis continued seeing Callas.

"He couldn't live without Maria," Kiki Feroudi Moutsatsos, Onassis' personal secretary, told People magazine in November.

"Maria was a piece of his soul, of his body, of his brain," Moutsatsos added. "That's why they never believed that they could be separate."

Onassis died of respiratory failure in 1975 at 69 years old. Historians believe that Callas and Kennedy never actually interacted, but they were aware of each other and were hostile.

According to Moutsatsos, Kennedy was "not happy" about Onassis' continued relationship with Callas but never spoke directly about the singer.

"What she spoke of was Onassis' behavior," Moutsatsos told People magazine. "If I could characterize her, I would say that she was behaving like a cat. Very smart. Very clever. She would wait for the right moment to speak with him about his behavior."

In her interview with Walters, Callas was asked about the rumors that she wasn't friends with Kennedy.

"I've never met her," Callas replied. "We're not friends, I've just never met her."

When asked if she harbored any bad feelings, the singer said, "Not at all. Why should I?"

"Maria" is now streaming on Netflix.