The couple's wedding was planned and officiated by Diana, reported Us magazine.
Ashlee, 29, wore a pearl-embellished wedding gown combined with USD 750,000-worth of Neil Lane jewelry and tiara. Her hair was styled in beachy waves.
Meanwhile, Evan wore a black velvet tuxedo with white silk trim. Ashlee's son, Bronx, walked her down the aisle.
Ashlee's older sister, Jessica Simpson, served as the matron of honour. Jessica's daughter Maxwell served as flower girl and her son Ace served as ring bearer.
This is the second marriage for Ashlee, who was previously married to Pete Wentz. Ashlee filed for divorce from Pete in 2011. Before dating Evan, Ashlee was linked to actor Vincent Piazza.