Christina and Nicole's sparklers

Diamonds are a girl's best friend — and that's certainly the case for Christina Aguilera and Nicole Richie.

The Dirrty superstar, 24, and her Simple Life pal, 23, both showed off their new engagement sparklers at Italian fashion designer Robert Cavalli’s boutique opening in Beverly Hills.

Christina is set to marry her long-term boyfriend, talent executive Jordan Bratman, after accepting his proposal at the weekend. And Nicole, whose dad is soul legend Lionel Richie, is to get wed to her DJ beau Adam Goldstein.

Bratman presented Christina with the $114,000 ring over a romantic proposal last Saturday at their hideaway abode in Los Angeles.

Nicole has been wearing her ring from Goldstein — whose professional name is DJ AM - since her 23rd birthday in September, but has been waiting for the past few months to officially announce their engagement.