Totalling three-and-a-half carats, the cushion-cut ring features carved diamond motifs in an art nouveau pattern. The ring's centre stone is an antique that dates back to the 19th century, according to a release from the jeweller.
"I feel like all my dreams are coming true," bride-to-be Cyrus tweeted hours after news of her engagement broke Wednesday.
The former Hannah Montana star first fell for the Australian hunk while filming 2009's The Last Song. Save for a brief split in August 2010, the couple has been together ever since.