Washington, Feb 16 - Nicole Richie and Joel Madden are set to wed at last.

The two have been together for more than three years and have two children. And now, they are making it official.

During a taping of the Late Show with David Letterman, Richie said that the couple is engaged to be married, a source tells People.

After the show, Richie headed to a New York restaurant-sans her fiancé - for dinner.

"She was glowing," says a source. "She was telling her table how happy she was."

Richie, 28, and Madden, 30, began dating in December 2006 and have daughter Harlow, 2, and son Sparrow, 5 months. (ANI)