Charlize Theron stopped answering Sean Penn's phone calls before their split during the 2015 Cannes Film Festival last month, multiple sources confirm exclusively to Us Weekly Credit: Dominique Charriau/WireImage

Straight to voicemail. Charlize Theron and Sean Penn appeared more in love than ever, but just like that, the Mad Max: Fury Road actress stopped picking up her phone. An insider close to Penn tells Us Weekly exclusively that Theron abruptly stopped speaking with the actor during the Cannes Film Festival last month.

"Charlize wasn't responding to his calls and texts," the source tells Us. "She just cut it off."

Us broke the news in December 2014 that the longtime friends became secretly engaged after a year of dating, and of their split on Wednesday. Theron, 39, and The Gunman actor, 54, kept close at Cannes in the south of France, which makes the news even more shocking.

"Sean and Charlize looked very happy together while at the Hotel Du Cap," a second onlooker tells Us, "with no signs of tension or a breakup."

The stars may not be speaking for now, but they will be bumping into each other in the future. Penn recently wrapped directing the drama The Last Face, which stars Theron.

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