The 35-year-old actress grew close to the 37-year-old star when they filmed 'The Giver' last year and they stayed in touch afterwards and are said to have enjoyed a string of meetings recently, reported Contactmusic.
"Their flirtation was one of the worst kept secrets on set. Nobody is surprised that they've been spending time together. They really enjoy each other's company," a source said.
Holmes, who has eight-year-old daughter Suri with ex-husband Tom Cruise, will be able to spend even more time with the 'True Blood' star in the coming months as they will be promoting their movie.