Jessica Simpson with an unidentified groomsman
10/14/2013 AT 01:30 PM EDT
sure can rock a bridesmaid dress.
The mom of two – she and fiancé Eric Johnson welcomed son Ace Knute
June 30 – walked down the aisle in publicist Lauren Auslander's wedding on Friday in Newport, Rhode Island.
If the bridesmaid look seems a bit familiar for Simpson, 33, it should … she was maid of honor
for best friend CaCee Cobb in December.
The day after the wedding, the Fashion Star
mentor, who also has a 17-month-old daughter, Maxwell
, with Johnson, Tweeted a photo
with her future mother-in-law.
Wrote Simpson: "Beautiful morning with my future mother-in-law and MoJo to my babies."
No final word yet on when she and Johnson will make it official!