One of those trips included the duchess’s daughter, Lady Louise, as the trio visited Peter Jones on King’s Road.
The insider said: “Louise adores Charlotte too, but doesn’t see as much of her as she is mostly away in Scotland.”
Lousie has just completed her second year at the University of St Andrews.
The source added that Charlotte’s mother, Princess Kate, is very pleased with her daughter’s close relationship with Sophie, coming as most needed during her recovery from cancer, which has “restricted her own outings”.
Charlotte will be able to spend more time with her favourite royal auntie as both families are set to head to Balmoral to spend some relaxing time together.
The royals traditionally spend late summer at the Scottish estate.
King Charles is said to have invited both the Prince and Princess of Wales with their children, the Duke and Duchess of Edinburgh with their family, as well as Princess Anne, her daughter Zara and husband Mike Tindall with their family, Peter Phillips and his daughters Savannah and Isla, and the Duke of York’s daughters Princess Beatrice and Princess Eugenie and their children.