Fame Flynet 1 / 13

Jessica Simpson walked down the aisle this weekend -- but she wasn't the one saying "I do" at the end of it. The pregnant "Fashion Star" mentor, 32, was a bridesmaid in pal Kathryn Syroka's wedding to Chris Hetherington in San Diego on June 15.

PHOTOS: Jessica's baby bump style

Dressed for the occasion in a black, curve-hugging gown with ruching and long sleeves, the second-time mom-to-be looked radiant and almost ready to pop. Her baby bump was on full display in the stretchy frock, and she smiled as she mingled with guests, including sister Ashlee Simpson, fiance Eric Johnson, also-pregnant BFF CaCee Cobb and actress Odette Annable.

PHOTOS: Jessica's body evolution

This was Simpson's second stint as a bridesmaid since Us Weekly revealed in November that she and Johnson are expecting their second child; she let slip in March that the baby would be a boy. (The couple are already parents to their daughter, Maxwell, 13 months.) The singer previously walked down the aisle as a bridesmaid at Cobb's nuptials with "Scrubs" actor Donald Faison in December.

PHOTOS: Jessica's daughter Maxwell

As Us Weekly exclusively reported in late May, the engaged star hopes to have a wedding of her own soon after welcoming her son this summer. During her April 14 baby shower, Simpson "was telling friends she wanted to get married a few months after the baby is born," a source told Us. "Jessica said, 'Let's have this wedding already before I get pregnant with another one!'"

PHOTOS: Jessica and Eric's romance

Simpson and Johnson have been engaged since 2010. "We've had two different wedding dates, but he keeps knocking me up," she quipped to Jay Leno early in her second pregnancy. "I'll just keep my legs crossed this time."


Bikini bumps: Pregnant celebs in swimwear

Stars who've been bridesmaids

Jessica Simpson's maternity style