01/02/2007 AT 10:20 AM EST
Good Charlotte's Benji Madden and Australian actress Sophie Monk are engaged, her rep tells PEOPLE exclusively.
"Benji proposed to Sophie in Australia on Christmas Eve," says Monk's publicist, Kacey Spies. "They are very excited and enjoying this time with family and friends."
Madden gave Monk a Neil Lane platinum diamond ring.
In September, Madden and Monk, both 27, were spotted kissing over lunch at L.A.'s Newsroom Café. That night, they stepped out again for dinner at The Ivy.
In October, Madden's twin brother, Joel, who recently split with Hilary Duff
, told PEOPLE of Monk, "I love (Benji's) girlfriend. She's so cool. I hang out with her, we have a great time. She's really similar to me – she's very care-free."
Added Madden, "(Love is) "the most rewarding thing in the world. It makes everything else in your life more rewarding. Your work, your family. Home, everything. It's great. It's a singer/songwriter thing – we're just hopeless romantics."
Monk appeared in Date Movie
and stars in the comedy Spring Breakdown,
in theaters April 13. Good Charlotte's next album will be released on March 20.