Why is the 'new' Van Gogh painting significant?

A previously unknown landscape painting by Vincent van Gogh has been identified by the Van Gogh Museum in Amsterdam.

Sunset at Montmajour - which depicts trees, bushes and sky - had spent years in a Norwegian private collector's attic after he had been told the work was not by the Dutch master.

Van Gogh museum director Axel Ruger explains to Emily Maitlis why the painting is so significant.