The 49-year-old actor, who has children Lily-Rose, 13 and Jack, 11, with former partner Vanessa Paradis, is said to be truly in love with his 'Rum Diaries' co-star, reported Contactmusic.
"Johnny is totally head over heels. He says that she is his soul mate and he plans to spend the rest of his life with her. Things are very serious between these two. He's told her that he wants to get married which is obviously a shock to anyone who knows Johnny," a source said.
"At first, Amber was a little apprehensive, because she didn't want to be seen as the mistress. But Johnny won her over with his generosity and he was constantly giving her gifts. On a weekly basis, Johnny would send her fresh flowers wherever she was. He also bought her tons of custom-designed jewels that would cost him up tens of thousands of dollars," the source said.