The handsome 27-year-old has appeared in The 40-year-old Virgin, and is best known for his recurring role as Dumptruck in ABC comedy-drama series Greek.
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His half-brothers are also actors. Chris Masterson played eldest brother Francis on Malcolm in the Middle while Danny Masterson appeared on That 70s Show.
The couple have a close circle of friends in Hollywood. One pal posted a picture of Dakota last week on a social networking site from a trip to Utah, and messaged Jordan: "Congrats 2 your girl on her HUGE role as Anastasia!"
Twenty-three-year-old Dakota is also close to Jordan's sister Alanna, who congratulated her after she won the role of Anastasia Steele, tweeting: "Everyone is so proud of you Dakota".
The pretty star has rarely spoken of her private life in the past. In October she did speak about her other half, but didn't mention his name. "I have a boyfriend that I've been with for a while. I've only been in long-term relationships. I've never really dated," she said.
Her personal life is sure to be in the spotlight now she's due to star in the much-talked about film. Until now, Dakota was best known for a part in The Social Network - in which she shared a love scene with Justin Timberlake - as well as appearances in 21 Jump Street, The Five-Year Engagement and Beastly.
She is the daughter of Don Johnson, star of TV shows Miami Vice and Nash Bridges, and his actress ex-wife Melanie Griffith.