The Prince of Wales has officially opened the largest new development at Eton College since it was founded 575 years ago.

Charles, whose sons the Duke of Cambridge and Prince Harry attended the exclusive private boys' school in Windsor, toured the £18.2 million Bekynton Field addition, which includes a 300-seat hall and 40 new classrooms and common rooms.

Architect John Simpson, who was responsible for The Queen's Gallery at Buckingham Palace, designed the development to blend in with the existing historic school and it features conservation-grade brickwork, stonework and brick arches.

The Prince, who has often been outspoken about architecture in the past, praised the development as he declared it officially open.

"The quality of the craftsmanship, the brickwork, the stonework, the copper and everything else is a great tribute I think, above all else, to those people who have these remarkable skills," Charles said.

The prince is also likely to have approved of the project's sustainable features. A ground source heat pump provides heating, drawing energy through a series of pipes under a nearby car park and the same pump reverses in the summer to cool the buildings.

The fountain's evaporation is also used to help keep the new Jafar exhibition gallery cool in the warmer months.

Eton College's head master, Tony Little said: "As this is such a major development we wanted to ensure we created a landmark building which will last for centuries, just as our other buildings have. We were delighted that the Prince of Wales was able to be our guest at the official opening ceremony."

On the apex of roof of the new Jafar Hall stands what has been described as "the largest and most complex" decorative copper feature constructed for a generation.

The hand beaten craft work, which is known as an akroterion, was made by Michael Johnson and Shelley Anderson from Newlyn Copper Works in Cornwall.

The Bekynton Field development, funded by Eton's supporters, houses the Modern Languages, Divinity and Economics and Politics departments and its Jafar Gallery is home to the Eton Museum of Antiquities - one of the world's finest private collections of Egyptian antiquities, bequeathed to the school by a former pupil.

Charles was tasked with placing the last piece - a marble head of a young man from a Greek relief, dating from the late 5th to early 4th century BC - in its display case to complete the exhibition.

The artefacts are used in an outreach programme for schools and researchers, which will be developed through the new gallery.

The Prince listened to pupils' poetry and drama recitals as he joined students in the Jafar Hall, and was particularly entertained by one boy's rendition of Eeyore's poem from AA Milne's The House At Pooh Corner.

Eton was founded in 1440 by King Henry VI as "Kynge's College of Our Ladye of Eton besyde Windesore" to provide free education to 70 poor boys. It is now one of the most exclusive private schools with fees costing over £34,000 a year.