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Beyoncé, Mariah Carey, Heartview Global Foundation

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It was a double diva kind of night for Beyoncé and Mariah Carey.

The two recently hung out together at a gala held by the Heartview Global Foundation, a heart disease research group, in Los Angeles. Both showed major cleavage in gorgeous dresses. Bey, 34, wore a sleek ivory, caped number and pearl drop earrings. Carey, 45, sported a semi-sheer, lace glittering gown, which she pared with a sparkling cuff and her massive diamond engagement ring.

"Two girls, one cause," Carey said on Instagram Thursday, alongside a photo of the two.

The two attended the event, which included dinner and an auction, to show their support for longtime friend and Heartview founder Jonathon Schwartz, who almost lost his life due to a heart condition, E! News has learned.

Beyoncé and Carey were seated at separate tables next to one another. Both were surrounded by friends.

"Mariah and Beyoncé spent a lot of time chatting and were seen having a good time together," a source told E! News exclusively. "They both seemed relaxed and enjoying themselves. They both took photos with guests as well as with each other."

During the auction, both bid on items and both bought portraits of Ray Charles, taken by Timothy White, which sold for $10,000 each. Bey also purchased a six-course chef's dinner for 12 friends for $15,000.

She and Carey have hung out before and even sang together at past events.

In 2008, Beyoncé performed onstage with Carey and other artists, such as Miley CyrusRihanna and Mary J. Blige, at Condé Nast's annual Fashion Rocks event at Radio City Music Hall in New York City.

Mariah Carey, Mary J. Blige, Beyonce

Larry Busacca/WireImage

In 2003, the two joined Donatella Versace at the designer's spring / summer fashion show during Milan Fashion Week.

Mariah Carey, Donatella Versace, Beyonce

PATRICK HERTZOG/AFP/Getty Images

Carey also showcased several sparkling gowns while performing at her Las Vegas residency show Mariah #1 To Infinity at Caesar's Palace. The singer is scheduled to put her show on hold between March and May to tour Europe and South Africa.

Beyoncé recently performed at the Super Bowl halftime show and announced a new world tour, following the release of her new song and music video "Formation."