One month after several sources confirmed to Us Weekly that the 26-year-old Drive star is planning to wed Mumford & Sons singer Marcus Mumford, 24, Mulligan showed off her dazzling engagement ring at the Sydney Airport in Australia Monday. See more photos of Carey's ring.
The future spouses -- who were childhood pen pals in London -- became engaged in August after five months of dating. "They're a great couple," a source told Us at the time. "Very sweet."
Mulligan split with longtime beau Shia LaBeouf in October 2010; Mumford broke up with singer Laura Marling later that year.