The actress was pictured out and about in Paris, France, as news of the split broke.
Emma appeared happy and relaxed as she stepped out with a female friend, opting for a casual look in a leather jacket, leggings, trainers and a baseball cap.
After shooting to fame as a child star playing Hermione Granger in the Harry Potter franchise, Emma graduated from Brown University in May 2014.
Knight received a Bachelor's in Ecology and Evolutionary Biology from Princeton in 2003, as well as an MBA from Columbia Business School in 2011.
Emma kept their relationship extremely private and would avoid talking about her boyfriend in interviews.
In February she told Vanity Fair: "I want to be consistent: I can't talk about my boyfriend in an interview and then expect people not to take paparazzi pictures of me walking around outside my home. You can't have it both ways."
She continued: "I've noticed, in Hollywood, who you're dating gets tied up into your film promotion and becomes part of the performance and the circus.
"I would hate anyone that I were with to feel like they were in any way part of a show or an act."
Things seemed to be serious between the couple as it was reported in February that the American businessman had introduced Emma to his parents.
His mother Katherine told the Daily Mirror newspaper at the time: "I have met Emma, and she's a wonderful girl. We don't see them very often because he's busy and working very hard."
The tech entrepreneur reportedly makes $150,000 a year and in his online profile, he writes that he is a "tech/entrepreneurship enthusiast, business school grad, writer, artist, photographer, adventurer, naturalist, etc."
Prior to her relationship with Knight, Emma dated British rugby player and Oxford University student Matthew Janney for a year.
The actress was previously linked to British singer and model George Craig, Oxford University student Will Adamowicz and financier Jay Barrymore.
In the past, Emma has joked that she looks as though she has had "6,000 boyfriends" because of the public interest surrounding her love life.
Speaking to Glamour magazine, she said: "Anyone I get photographed with is automatically my boyfriend. So it just makes it look as if I've had, like, 6,000 boyfriends!"
