David Oyelowo and Rosamund Pike in A United Kingdom

Gear up for the greatest love story you’ve never heard of. It’s the late 1940s and Prince Seretse Khama, the heir to the throne of Botswana has fallen in love and married a young, white English girl named Ruth Williams. Their interracial love affair is so scandalous, Seretse and his bride must spend six years in exile in London, banned from Khama’s own country because he married a white woman.

Selma star David Oyelowo first discovered the couple’s story in 2010 when he read Susan Williams’ book The Colour Bar and he’s been on an obsessed path ever since to get it turned into a movie.

“I was so struck by the level of challenge they faced simply for falling in love with each other that I became completely intoxicated with it,” says Oyelowo who plays Seretse. “I also realized in reading the story I had never seen an African love story of this cinematic scope. It spoke to me as an African, as a man, as a romantic.”

So, for six years, Oyelowo worked tirelessly to turn The Colour Bar into A United Kingdom, written by Guy Hibbert (Five Minutes of Heaven) and directed by Belle helmer Amma Asante. British distributor Pathe (Selma) financed and will release it internationally.

In addition to collecting producers during every film Oyelowo shot (Rick McCallum from Red Tails, Brunson Green from The Help), he had to recruit Pike to play his bride. That opportunity came when Oyelowo was on set in Uganda and discovered via the trades that Pike’s upcoming movie, The Deep Blue Good-By had been shuttered suddenly after her costar Christian Bale tore up the ligaments in his knee.

“I went straight to my computer and I sent her images of these two people with the note ‘Take a look. Tell me what you think,'” he says. “She wrote me back the most impassioned e-mail: ‘I don’t know who these people are. I don’t know what they’ve done with their lives. But I’m so moved by them, tell me more.'”

Oyelowo’s fervor over this couple and their story is certainly contagious, but his own relationship to them is likely rooted in the fact that he found some echoes between his life and Seretse’s: he also is from his own royal family in Nigeria and is married to white actress Jessica Oyelowo.

“Yes, I’m married to a white lady who I love deeply. We haven’t had the struggle they’ve had, but I feel so blessed that I live in an era where me being married to whom I’m married to isn’t illegal or frowned upon, literally, by nations in addition to individual people,” says Oyelowo. “Let’s not be naive. There are people out there who don’t love a black person and a white person being married, but it’s certainly not what Seretse and Ruth experienced. This film is a celebration of two people I deem so brave for doing what in my life, I’ve been able to take for granted.”

And it seems the love between Seretse and Ruth was able to move disparate cultures and countries. “They ended up reshaping their nation through their love,” adds Oyelowo. “Botswana is a different country for the fact that these two people got married. It has a different relationship to race, partly because of them. That in and of itself is miraculous.”

Pathe plans to take A United Kingdom to the Berlin Film Festival and is anticipating a fall release.