Among the earliest – and most famous – sufferers was King Charles VI of France, who reigned from 1380 until his death in 1422, suffering from various bouts of ‘madness’. The belief he was made of glass was so powerful, he’s thought to have had a special suit of iron ribs fitted in his clothes to protect his delicate body, and wouldn’t allow people to touch him.

Strangely, the glass delusion went into decline around the middle of the 19th Century, before almost completely vanishing. No-one really knows why – although there are very occasional modern instances of it recorded, most recently in 2015 by a psychiatrist in the Netherlands.

Fragile, pure and chaste

Today, the delusion is approached as a mental health issue – and it was this which made Sobler convinced it would be a rich topic for a play. “I really took it as a jumping-off point: it’s definitely not a historically accurate depiction,” she caveats her answers by saying, but adds that she thought the image of having a glass piano inside you was a really interesting metaphor. “How do we relate to it today? What does it represent, in our anxieties, today?”

Sobler suggests that the psychological patterns behind the glass delusion are still with us. “I suffer with anxiety, it’s extreme,” she says. “And I am very capable of talking myself into a belief: if I find a spot on my body, I can really talk myself into that being a disaster.” While swallowing a grand piano is an extreme case, Sobler says that she too has the capacity to “form an idea in my head, talk myself into it, and create my own reality around it. That’s one of the things that really drew me to [Princess Alexandra].”