On a combined journey to view Spanish art treasures, the heir to the throne kissed the Queen Consort on both cheeks and on her hand as he greeted her to 900-year-old Auckland Castle, one of Europe’s best-preserved bishops’ castles.

After the Spanish queen came in an Audi A6 with the registration plate SPA IN, Charles, 73, and Letizia, 49, formally launched a new art gallery dedicated to Spanish art and culture, the only one in the UK.

The Spanish Gallery is part of the Auckland Project, a unique redevelopment effort that uses art, spirituality, and legacy to attract visitors to Bishop Auckland.

It consists of galleries, gardens, and parks, as well as the outstanding Kynren historical re-enactment events, which are conducted throughout the summer.

The project was created by philanthropist Jonathan Ruffer and his wife Jane, however Mr Ruffer was unable to tour the two royals around due to his isolation, which he saw from an upper window of his residence near the castle gates.

Auckland Castle, formerly home to the powerful Prince Bishops of Durham, reopened on March 23 after completing substantial restoration work that restored its royal chambers to their full Georgian Gothic glory.

The castle has 13 life-sized statues painted by Francisco de Zurbaran that were brought by Bishop Trevor in 1756 and have since displayed in the Long Dining Room.

Mr Ruffer prevented the Zurburans from being sold by donating £15 million to the Church of England, which sparked the rehabilitation effort.

He also funded the new Spanish Gallery in town, where Charles and Letizia saw masterpieces like as El Greco’s The Holy Family and Bartolome Esteban Murillo’s Cherubs Scattering Flowers.

Schoolchildren shouted as the royal entourage emerged from the gallery, waving British and Spanish flags.