Pregnant Jessica Simpson and her sister Ashlee turned bridesmaids on Saturday (25Mar12) to celebrate their best friend's wedding in California.

The pop star-turned-fashion designer and her sibling donned pastel gowns and looked on as their former assistant Lauren Zelman married TV actor Bret Harrison at the Parker Palm Springs.

Heavily pregnant Jessica, who is due to give birth any day, appeared tobe in good spirits as she arrived at the outdoor ceremony with her former footballer fiance Eric Johnson.

A source tells UsMagazine.com, "She was a good sport about being a bridesmaid even though she is so pregnant. It definitely wasn't easy for her to get around and help the bride".

Singer/actress Ashlee Simpson was escorted to the event by her Boardwalk Empire star boyfriend Vincent Piazza, and her three-year-old son with ex-husband Pete Wentz, Bronx, stole the show as he served as the bride andgroom's ring-bearer.

Former The O.C. actor Adam Brody, who plays in rock band Big Japan withHarrison, was also a member of the wedding party.