The Keeper of the Queen's Pictures and Soviet spy sought out kindred spirits among artists who, like him, had lived double lives

Matisse’s cut-outs are free from the brooding and nostalgia that haunt the late works of so many artists

Marxist art historians cherish his Cubism, but he later became a true artist, not just a modernist

Sterling Clark's collection of French art, on show at the Royal Academy, is as appetising as it is unfamiliar