Dr Karen Serres, curator at the Courtauld, told the Telegraph: ‘The work was never loaned but managed to procure it. They never attempted a proper study.
“If you think about it, people come to see Van Gogh – it’s ‘box office’ so it stays on the wall for people to see. But then you never get the chance to study it.
“By putting it next to another self-portrait of him in a straw hat, we noticed that the painting seemed a little small in comparison, and his hat a little truncated.
“While studying it, our restorer realized it was actually bigger, and someone tore off part of the portrait at one point.”
The painting may have been broken off to fit the frame
Nestled in a large frame, damage to the artwork was not immediately obvious, but experts found the painting – done on a thin board – had been broken at some point in its history, may -be to adapt it to its frame.
The damage cut off the left side of Van Gogh‘s hat – on the right side of the painting.
The city of Detroit bought Self-Portrait with a Straw hat in 1922 when the auto industry was booming, but amid financial difficulties in 2014 authorities considered selling the painting which was then valued at a low of £90 million by Christie’s.