A Texan man was shocked to discover the painting that was hanging behind a door in his home office is worth between $800,000 and $1million.

Rue Ferguson took the painting that his great grandparents bought back in 1920 to a taping of Antiques Roadshow to learn that it was actually a major work in the career of famous Mexican artist Diego Rivera.

'My mind went blank when she told me what the value was,' Mr Ferguson said following the television hosts' appraisal.