Jessica Biel CHOPS her long locks into a bob after book signing in Studio City trends now

Jessica Biel unveiled a dramatic hair transformation - from chest-length locks to a short bob - on Saturday evening.

The 42-year-old Emmy nominee - who boasts 19.4M social media followers - captioned her before/after video: 'Brought back the f*** a** bob.'

Jessica - who previously had a bob in 1998 and 2006 - enlisted Milbon global creative director Anh Co Tran to cut of her long signature mane.

Earlier that same afternoon, Biel stopped by independent bookstore Annabelle's Book Club LA in Studio City to attend an hour-and-a-half-long book signing event.

The former Cruel Summer producer wore a seafoam-colored blouse, blue jeans, and white pumps to promote her 64-page literary debut A Kids Book About Periods, which hit shelves last Tuesday.

Jessica is mother to two sons - Silas, 9; and Phineas, 3 - and she is impressed with how well her eldest child reacted to her menstruation manual created for children aged 7-9.

'He kind of was like, "Oh, that's weird." I said,

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