Anna Nicole Smith's daughter Dannielynn Birkhead's all grown up ... rocking an outfit previously worn by Janet Jackson and attending Kentucky Derby events with her dad, Larry.

The 17-year-old appeared in Larry's recent Instagram post ... smiling in a couple cute father-daughter pics on the way to the Barnstable-Brown Gala -- a star-studded lead-up to Saturday's big race.

Check out the pic ... Dannielynn's in a full black get-up here, covered in zippers Larry said he bought from Julien's -- a popular auction house.

Julien's describes the dress as a "Gianfranco Ferre black dress that's knee-length in the front and floor-length in the back and features zippers all around." It recently sold for $780 on the site.

The pics are a rare glimpse into the Birkheads' lives ... they generally avoid media attention though they reportedly have made a tradition of attending the Kentucky Derby together -- hitting the biggest day in horseracing every year since Dannie was 3.

And, Janet Jackson chic seems like Dannielynn's fashion method of choice for the annual soiree ... remember, when she and Larry attended the Derby in 2022, she wore another Jackson special -- and, even got to take a pic with JJ while in it.

Of course, Dannielynn was just months old when her mother was discovered unconscious in her Florida hotel room in February 2007. Her death was ruled an accidental overdose ... she was just 39.

Pretty wild to see Dannielynn growing up so quick ... enjoy the Derby, you two!