In an interview with Today's Savannah Guthrie, set to air on Friday, he said of the blonde actress: "She's sharp as a tack. A southern belle and sweet as can be, and very good for me."
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Amber and Johnny first met while they filmed The Rum Diaries together in 2012.
Johnny was still wearing Amber's diamond engagement ring, and when Savannah pointed it out and told him: "I think you look engaged," he clicked his fingers.
In an interview with David Letterman aired on Thursday, the star mentioned the sparkler again, saying, "it was too big for my girl".
He also told the legendary interviewer that he "gets along well" with his future father-in-law.
The actor has taken to wearing Amber's diamond engagement ring. He told David Letterman: "It was too big for my girl."
Johnny, 50, said that Amber's father David is "about the closest thing to Hunter S. Thompson I’ve ever met", referring to the excentric and wild author who wrote books The Rum Diares and Fear and Loathing in Las Vegas on which Johnny's films are based.
While he's confirmed the engagement, the Hollywood star sidestepped a question about potential wedding plans while on the promotional trail in China for his new film Transcendence.
"I think that I would be better at making women's shoes than I would be at wedding planning, I can't plan anything," he admitted. "I'm really bad at that stuff."
It will be the first marriage for Amber, and the second for Johnny, who was married to Lori Anne Allison for two years in the mid-80s. He was in a relationship with Vanessa Paradis, the mother of his two children Lily-Rose, 14, and Jack, 11, for 14 years before they announced their split in June 2012.