Pierre Bergé, the Yves Saint Laurent co-founder and longtime partner of the late designer, died early Friday at his home in Saint-Rémy-de-Provence at age 86, according to an announcement by the Fondation Pierre Bergé-Yves Saint Laurent. Bergé had suffered from myopathy, a disorder of the muscular tissue, which he made public nearly 10 years ago; he died in his sleep “following a long illness,” the announcement reported.

“It is with a deep emotion that I have learned of Pierre Bergé’s passing,” wrote Anthony Vaccarello, Saint Laurent’s current artistic director, in a statement Friday. “He welcomed me with kindness since my first day at Saint Laurent. His advice and his support have always guided me.”

Bergé and Saint Laurent met in 1958, when the designer was still at Christian Dior. They were 29 and 23, respectively. Three years later, they founded his eponymous brand, Yves Saint Laurent, for which Bergé acted as the business mind behind the operation; he steered the label to profitability, and notoriety, over the next several decades. (Their sometimes-contentious relationship has been the subject of several films; in Yves Saint Laurent, Bergé is played by French actor Guillaume Gallienne, while in Saint Laurent, it’s Belgian actor Jérémie Renier. Both films premiered in 2014, but only Yves Saint Laurent received Bergé's stamp of approval.)

With Saint Laurent’s death in 2008, Bergé set about securing the designer’s legacy; he had planned to inaugurate two new museums dedicated to Saint Laurent, one in Paris and one in Marrakech, this fall. “I am infinitely sad that he will not be able to attend the opening of the two museums in Paris and Marrakech that he cared about so much,” Vaccarello wrote in his statement. “A great figure in French culture has left us.” (Bergé also married Madison Cox, the director of the Fondation Jardin Majorelle in Marrakech, earlier this year.) And he remained close with the brand, regularly making appearances at Saint Laurent’s Paris Fashion Week shows (though, as Vogue noted, he was “dismissive of Tom Ford,” who designed for YSL from 1999 to 2004) alongside the likes of longtime Saint Laurent muses Catherine Deneuve, Jane Birkin, and her daughters Lou Doillon and Charlotte Gainsbourg.

Beyond fashion, he secured a position as president of the Opéra Bastille in Paris from 1989 to 1994, and after that, as an honorary director of the city’s national opera, thanks in part to his friendship with the former French president François Mittérand, of whom Bergé was an outspoken supporter. Bergé was also known as a prominent leftist and activist; in 1994, he co-founded Sidaction, the French organization that raises awareness about and funds for HIV/AIDS research.

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It’s a somber moment in the midst of New York Fashion Week, and the likes of Vaccarello, editor Carine Roitfeld, Saint Laurent muse Marisa Berenson, and fellow designer Francesco Scognamiglio took to Instagram to post remembrances of the late fashion and arts patron.

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Merci Pierre

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À toi cher Pierre, Tu as rejoint Yves, un homme que tu as tant aimé... pour qui tu as tout donné... quel bel Amour... ta passion, ta force, ta détermination, ton goût impeccable, ta générosité, ton génie font de toi un grand homme, un homme exceptionnel. Tu nous laisse avec un grand vide mais avec de très beaux souvenirs et un patrimoine qui est un trésors pour le monde. Ta dernière grande oeuvre les musées Yves Saint Laurent à Paris et à Marrakesh seront les lieux sacrés pour votre mémoire. Rest in peace dear Pierre. Avec beaucoup d'amour et de lumière Marisa 〰〰〰 To you dear Pierre, You have joined Yves, the man you love so much... to whom you gave your life... what a beautiful and powerful Love... your passion your strength, your determination, your impeccable taste, your generosity, your genius make you a great man, an exceptional man. You will leave a great void, but many wonderful memories and a heritage that is a treasure for the world. Your last masterpiece the YSL museums in Paris and Marrakesh will be sacred places for both your memories. I will miss you Pierre... Rest in Peace and joy. I send you much love and light. Marisa🙏😇❤️💜💛💚💙🌟🌺🌸🌺🌸🌺🌸🌺🌸🌺 Mes pensées, mon Amour et mes prières pour Madison Cox, Son mari bien aimé et Ange gardien. My love, thoughts and prayers are with Madison Cox , his beloved husband and gardian Angel.😇❤️ #pierrebergé #restinpeace

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Aujourd'hui j'ai perdu un ami. Adieu Pierre

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