Actor George Clooney and singer-songwriter Chris Cornell attended the London premiere of the Armenian genocide film The Promise.

Chris Cornell, who composed the theme song for the film, posted a photo on Twitter.

Elton John, Cher, Barbara Streisand, Andre Agassi, Sylvester Stalonner, Dean Cain and Leonardo DiCaprio have all expressed their support for the film.

The Promise,” which world-premiered at the Toronto Film Festival last September, will go on wide release in the U.S. on 2,000 screens via Open Road Films on April 21.

The roughly $100-million film is considered a breakthrough after several attempts to make a Hollywood film about the Armenian genocide failed during past decades.

“The Promise” centers on a love story involving a medical student (Oscar Isaac), a journalist (Christian Bale), and the Armenian woman (Charlotte Le Bon) who steals their hearts. All three find themselves grappling with the Ottomans’ decision to begin rounding up and persecuting Armenians.