Their wedding's on the way!

Ashlee Simpson and Evan Ross celebrated their engagement with a big party on Wednesday night, which was attended by friends and family, including big sis Jessica Simpson.

"What an amazing engagement party with all of our loved ones! We gettin' married," the 29-year-old singer tweeted after the soiree.

She also shared a photo of her snuggling up to her 25-year-old fiance, who popped the question during a trip to Hawaii in January. In the pic, Ashlee can be seen dressed like a flapper with a feathered headband on, while Evan sports a very furry jacket.

Jessica also posted a photo from the bash, showing off her recent weight loss in a sexy, tight white mini.

"Celebrating my best friend and sister missbananahammock @ashleesimpson. I love her so much," Jess tweeted from the event.

No word yet on when the two will tie the knot, but it will be the second wedding for Ashlee. She was previously hitched to Pete Wentz from 2008-2011, they have one son together.

Jessica will be walking down the aisle this year too with fiance Eric Johnson. Who do you think will say "I Do" first?!

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