By Nesserine Fellah

LONDON (Thomson Reuters Foundation) - The true story of a teenager from a Ugandan slum who transformed her life from corn seller to international chess player is to make its European premiere at the London Film Festival in October.

The Disney movie, "Queen of Katwe", is based on the life of Phiona Mutesi who turned up at a sports outreach program in Katwe in Kampala for a cup of porridge aged about nine in around 2005 and was drawn into a world of knights and checkmates.

Now Uganda's No. 3 female chess player according to the World Chess Federation, Mutesi is hailed an inspiration to many girls for managing to escape the life of poverty she was leading on the streets with her mother after her father died of AIDS.

Uganda is one of the poorest countries in the world with 2014 government figures showing nearly 20 percent of the 38 million population lives in poverty. UNICEF data shows 24 percent of Ugandan children under five live in extreme poverty.

The movie, to be shown on Oct. 9 after opening in the United State in September, stars newcomer Madina Nalwanga as Mutesi, Oscar-winning actress Lupita Nyong'o as her mother, and David Oyelowo as her chess teacher, a soccer player turned missionary.

Oyelowo, who played Martin Luther King Jr in "Selma", praised the film for illustrating a good side of the impoverished east African country.

"Africa is teeming with amazing people who in spite of their, at times, difficult lives, manage to remain full of joy and hope," Oyelowo said in a statement.

"This is a story where the impossible is made possible through family, mentorship, encouragement, hard work, and faith, all things we can aspire to."

The film is based on a 2012 book about Mutesi who used the money she received from film rights to buy land for her family and to continue her studies, aiming to become a paediatrician, according to online chess community chessgames.com.

Mutesi, who spoke at the Women of the World Summit in New York in 2013 about the obstacles she had overcome, held the first ever all-girls chess clinic in Uganda with more than 400 girls showing up to the clinic.

But the girls weren't only taught chess but also learned about delaying marriage and children until after they finished school and started their careers, according to her website.

Uganda has one of the world's highest rates of pre-teen and teenage pregnancies with one in every four girls aged between 15 and 19 getting pregnant, according to the Bureau of Statistics, and nearly half of girls married before 18.

The BFI London Film Festival, which celebrates its 60th anniversary this year, is Britain's largest film festival that showcases new British and international films.

(Editing by Belinda Goldsmith @BeeGoldsmith; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, property rights and climate change. Visit http://news.trust.org)