Ashlee Simpson has gone back to her roots -- literally!

After promising that he would "try and sneak a pic to post" of Simpson's sassy new blonde pixie cut, Pete Wentz followed through when he uploaded a photo of Simpson and son Bronx, nearly 2, Tuesday afternoon.

"Yah fam headed out tonight stoked!" Wentz, 31, tweeted. "Cute hair mama!"

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Simpson (who is a natural blonde) was most recently seen with long, ombre-style hair -- though the 26-year-old has also rocked black, brown and red shades in the past.

Wentz's thoughts on his wife's new 'do?

"New blonde pixie haircut is cute!" he tweeted.