Nicole Richie and Joel Madden are engaged!

Nicole Richie's three years relationship with rocker beau Joel Madden's is still going smooth and they are now ready to walk the aisle.

According to USmag, Richie said Monday night during a taping of the Late Show with David Letterman that she and Joel are engaged to be married.

Yep. i'm engaged. Very happy," wrote Madden, 30, on Twitter Monday. "Yeah we've been engaged for a while so your all kind of late on that. But Thanks for the hooplah all the same."

The couple started dating in December 2006 and they have two children, Harlow, 2, and Sparrow, 5 months.

[Photo courtesy by Frederick M. Brown/Getty Images]