Royal expert Marlene Koenig explained this decision was made to avoid any ill feelings towards Camilla.
She told Town and Country magazine: “Camilla was not popular or well-liked, [though] this has changed a lot since the marriage as Camilla has taken on a lot of patronages and Charles is a lot happier.
“Still, [there was] a lot of tension and anger among a certain element of the population—so it was decided that Camilla would be styled as the Duchess of Cornwall, even though, of course, she is the Princess of Wales.”
Despite Camilla’s popularity increasing in recent years, she still uses the Duchess of Cornwall style.