A source tells PEOPLE that the couple, who had shared a London home overlooking Hyde Park, quietly broke up a few months ago, shortly after Knightley bought a house in the South of France, outside Nice.
Distance and career "were both considerations," the source says. "It was time for her to move on."
Will Knightley, Keira's father, tells the British tabloid the Sun: "They were together for quite a long time, and it is always hard breaking up. She's focused on her work."
Knightley, 25, is best known for playing Elizabeth Swann in the Pirates of the Caribbean movies. Friend, 29, played Prince Albert in 2009's The Young Victoria.