The pictures, all by the renowned royalty and fashion photographer Terence Donovan will be on show at the National Portrait Gallery in London.

The photographs are from a selection taken by Mr Donovan, who died in 1996, at four official sittings between 1986 and 1990.

One of Donovan's portraits, taken in 1987

They were presented to the gallery by Diana Donovan, the photographer's widow.

Although the studio portraits were officially commissioned, several of the less formal ones are said to document the close friendship between the Princess and Mr Donovan.