“We need to invest in these young people before Isis does,” says Abdulnasser Gharem, a former lieutenant colonel in the Saudi Arabian army, sipping a glass of water in the Tate during a flying visit to London. “They have energy and have little to do in their own country – so what would you expect them to do?”

Gharem, who was in the same class at school as two of the 9/11 hijackers, is one of the Middle East’s biggest-selling artists. At Christie’s in 2011, he sold Message, Messenger – a sculpture symbolising the Dome of the Rock in Jerusalem – for more than $800,000, a record-breaking price for contemporary Middle Eastern art at the time.

He’s now on a mission to lure the young away from terrorism – by encouraging them to become artists instead. With his younger brother Aljan, he has set up a foundation at his studio in Riyadh to mentor people accordingly. So far, the studio has 11 students, aged 18 to 22, whose works will be on display in London next month. He refuses to identify the jihadists he knew as a teenager, but says the only way to conquer the wave of terrorism sweeping the Middle East – and with it the world – is to encourage people to think “individually”.