Princess Anne was forced to cancel an engagement in Peterhead yesterday after she was taken to hospital when she became unwell.
The Princess Royal was due to visit HMP Grampian on Thursday September 8.
She would have been the first member of the Royal Family to visit the Peterhead prison.
It is understood that Princess Anne was taken to ARI after feeling unwell and cancelled engagements at the advice of doctors.
Buckingham Palace said the 66-year-old Princess had been suffering from a bad chest infection.
The Queen’s daughter has been staying at Balmoral in Aberdeenshire and attended the Braemar Gathering at the weekend before taking unwell.