The groom-to-be shared the news with fans via his Facebook.com page on Thursday (14Aug14), when he uploaded a photo of the couple, with actress Keough showing off her ring.
In the accompanying caption, he wrote, "So that happened".
Keough met her beau while working on Mad Max: Fury Road in 2012, and a source tells UsMagazine.com, "They're very serious. They're perfect for each other. Great people."
The 25 year old daughter of Lisa Marie Presley and her ex-husband Danny Keough was previously engaged to wed her Magic Mike co-star Alex Pettyfer in early 2012.
Recent reports suggested she was back in the arms of ex-boyfriend Ryan Cabrera after her split from the actor.