The Clarks' marriage was devoted but stormy. Clark was a womaniser, and although Jane had love affairs, notably with the composer William Walton, she took some of her husband's extramarital relationships badly. She suffered severe mood swings and later alcoholism and a stroke. Clark remained firmly supportive of his wife during her decline. The Clarks' relations with their three children were sometimes difficult, particularly with their elder son, Alan. He was regarded by his father as a fascist by conviction though also as the ablest member of the Clark family "parents included"; he became a Conservative member of parliament and junior minister, and a celebrated diarist. The younger son, Colin, became a film-maker, who among other work directed his father in television series in the 1970s. The twin daughter, Colette, became an official and board member of the Royal Opera House; she outlived her parents and brothers, and was the key source for James Stourton's authorised biography of her father, published in 2016.