The oil painting, by American specialist Todd Bright, shows the overdue queen as taken by photographer Mario Testino.
Hepplestone Fine Art in Chorley, Lancashire, was chosen to sell the painting, eligible Diana, which is predicted to increase £100,000.
The cash will go to the Diana Prize non-profit organisation, which honors the perform of adolescents in community.
Mr Bright said: “Princess Diana motivated so many individuals in her lifestyle, and it made sense to me to give the portrait to the Diana Prize to help increase cash that will go towards motivating adolescents in their own perform, whether innovative, non-profit or business.”
Maggie Turner OBE and us president of the Diana Prize said: “We are incredibly thankful to Todd Bright for giving us the opportunity to increase more cash so that we can continue our work.
“The portrait works as a memory of Diana’s interest for lifestyle and fun.”