Frida Kahlo is regarded as one of Mexico's greatest painters: her extraordinary personal style, her tragic story, her relationship with Diego Rivera (the more famous painter in their day) alongside her passionate paintings have made her a cult figure since she died over sixty years ago.But beyond the familiar images there is a private story about a daughter who confided in her beloved mama, Matilde Calderon Kahlo. Until now Frida's handwritten letters have only been available to sc...