Spears took to Instagram to share a glimpse at her In The Zone-era body -- a throwback shot from that epic topless Mark Rolston photo shoot for the October 2, 2003 issue of Rolling Stone. You know the one.
"My friends sent me this picture today… and it's weird because I just realized it's one of the only pictures I've ever taken upside down!" the 34-year-old captioned the revealing snap.
The racy photo from the same era that brought us "Toxic" isn't such a far cry from Spears' current physique, as she recently told Ryan Seacrest that she is the fittest she's been in "probably 20 years."