Two years ago the elderly couple traded their A-listed castle for a bungalow in a nearby village when the practicalities of living there became too much. Their story is portrayed in a BBC documentary broadcast this week. On moving back to Scotland from Africa in the 1970s, the pair bought the ruined Inverquharity Castle in Angus. Over many years, they rebuilt and painstakingly restored it.
Mrs Grant admitted that when she bought the house, she had envisaged living there for the rest of her days. "I didn't know then what it felt like to find the stairs an absolute obstacle," she said.
Having suffered a minor stroke, Mr Grant's health was not what it once was and the pressure of maintaining such a large, old property, along with 11 acres of land, became untenable.
Film-maker Darren Hercher, a friend of the couple, persuaded them to allow him to capture their last months in the 15th century tower house near Kirriemuir.
l Keys to the Castle is on BBC Two Scotland, 9pm, on Thursday.