The singer-actress and the grungy rocker reportedly began dating at the end of 2007 and split during summer 2008 before getting back together in recent weeks.
“Mandy is one of those genuinely sweet angelic people you wish to meet your whole life,” Ryan said in a statement issued in August to confirm the break-up. “Unfortunately I am allergic to paparazzi.”
And while Mandy’s camp has confirmed the engagement, the musician remains private.
“We have no statement and never comment on Ryan’s personal life,” a rep for Ryan told Access Hollywood on Wednesday.
Since their split – and since spending time with ex DJ AM — Mandy has been spotted on tour with the “New York, New York” singer, who is set to release his first book, poetry collection “Infinity Blues,” on April 1. Mandy’s next album, “Amanda Leigh,” is due on May 26.
Mandy was previously linked to the DJ and tennis star Andy Roddick, while Ryan has dated Parker Posey, Winona Ryder and singer Beth Orton, among others.
They’re the second rocker-actress couple to get engaged in the last few months – Death Cab for Cutie frontman Ben Gibbard and Zooey Deschanel, who also fronts retro-pop act She & Him, announced their engagement just before New Year’s.