Obit in the Times of 10 June 2021, where his brief first marriage is mentioned:
Alistair Buchanan obituary
Banker who helped to restore his family’s former seat, Nymans, into a flourishing garden attraction after the Great Storm of 1987
... his cousin Anne, the Countess of Rosse, had passed him the mantle of “family representative” of Nymans, the family estate in West Sussex that had passed to the National Trust in 1953. After the destruction of the gothic mansion in a fire in 1947 the gardens remained as a tourist attraction but, shaded by a gloomy canopy that the gardeners were too conservative to thin, they attracted less than 30,000 people a year.
...Alistair Buchanan was born in London in 1935, the son of Phoebe and John, who was chairman of Allen, Harvey and Ross, the bank. He later said that “we children did not see much of our parents. Father and mother travelled a lot, to all parts of the world, sending back postcards with loving messages.” One fond memory from his early childhood was that of his mother playing the piano, while his father smoked and looked on benignly.
...At Oxford he had become enamoured of his second cousin, Louise Parker. They married shortly after his graduation, but in the second tragedy of Buchanan’s young life, Louise died two years later of Hodgkin’s disease. ...At a dinner party he met Ann Baring; she read his palms, including his love lines, and in 1963 they married. They had three daughters: Katie, who went on to make documentaries; Tessa, who became a civil servant; and Helen, who became a lawyer. Buchanan encouraged Ann to pursue her academic research into the wellbeing of children, and immerse herself in the life of St Hilda’s College, Oxford, where she became a fellow.
Alistair Buchanan, banker and gardener, was born on December 13, 1935. He died of heart failure on March 6, 2021, aged 85https://www.thetimes.co.uk/article/alistair-buchanan-obituary-2zcgghbhn