Jessica Alba and Topher Grace are among the celebrity guests attending Jessica Simpson's wedding celebrations.

The 33-year-old star is marrying former NFL star Eric Johnson at San Ysidro Ranch in Montecito, California today (05.07.14) and invited a few of her long-time showbiz pals to attend their four days of festivities.

The 'Sin City' actress, who starred in 'The Love Guru' with Jessica in 2008, was spotted at the couple's Independence Day barbecue on Friday (04.07.14) with her husband, Cash Warren, and daughters Honor, six, and Haven, three.

An eyewitness told E! News that the brunette beauty looked ''effortlessly radiant and beautiful,'' as she spoke to a starstruck teenage guest.

Topher, who bonded with the bride-to-be when she guest-starred alongside him on 'That 70s Show' several times, was also there with his actress girlfriend, Ashley Hindshaw.

After the barbecue, the group boarded buses to the nearby Four Seasons La Pacifica hotel's ballroom and terrace, where they watched a fireworks display.

Speaking about Alba and her family, a source said: ''They blended in with other families as they left the fireworks show. Even after a long day, they looked amazing.''

It was previously revealed that the 'Sweetest Skin' hitmaker sent a strict email to her guests, instructing them not to bring any cell phones or cameras to the wedding, as they have inked a lucrative deal with a magazine to publish the photographs.

The Weight Watchers spokesperson, who announced she was engaged to Eric in November 2010, kicked off their celebrations with a rehearsal dinner on Thursday night (03.07.14) and is expected to host a final brunch tomorrow (06.07.14).