James Allen News Center

Nicole Richie has officially confirmed that she is engaged to boyfriend Joel Madden of Good Charlotte. The 28-year-old socialite and daughter of Lionel Richie confirmed the engagement during a taping of The Late Show With David Letterman on Monday, after David asked her is she and Joel were married.

Letterman asked Richie: "You're not married yet, is that correct?"

"We're not married," she answered.

"Are you engaged?  Are you planning to get married?" Letterman persisted.

"We actually recently are engaged, yes," Richie replied.

Earlier during the week, Joel revealed that he and Nicole were engaged via Twitter.

So, what`s the round diamond engagement ring like? According to jewelry and style expert Michael O` Connor, the ring "is classic with a modern twist. Classic because it contains a brilliant cut center stone (approximately 3-4 carats) set in platinum, but the pave diamonds surrounding the center stone makes it modern. I would estimate the ring's value between $60,000 - $85,000.

"This diamond is set in platinum so it makes the diamond sparkle brighter. Also, Nicole won't have to worry about the large diamond falling out since platinum settings hold stones more securely than other metals."

A source told UsMagazine.com Monday, "Nicole and Joel are in the process of planning the wedding. She's very involved in every detail. She's thrilled."

The couple has been dating since 2006. They have two children: daughter Harlow and son Sparrow.