Joel Madden and Nicole Richie Joel Madden and Nicole Richie

Longtime couple Nicole Richie and Joel Madden are engaged, People reports.

Richie, 28, showed off her ring and announced the engagement during a Monday taping of The Late Show with David Letterman, a source told the magazine. The episode is scheduled to air Friday, but Madden, 30, couldn't keep the news to himself for long.

Nicole Richie to star in ABC sitcom

Nicole Richie and Joel Madden introduce son Sparrow