1. Ariana Grande shared this screen grab from a video taken of her in 1996:
2. Isla Fisher welcomed Courteney Cox onto Instagram by sharing this photo of the two of them doing karaoke in the early '00s:
3. Amy Schumer shared her adorable baby photo from 1981:
4. Madonna (on the right) posted this photo of herself at her high school graduation in the mid-'70s:
5. Kal Penn posted this clip of himself in a The Lonely Island video circa mid-'00s:
Hi 👋🏾 dudes! #TBT @jormataccone @andysamberg @akivaschaffer @thelonelyisland
6. Megan Mullally shared this photo from 2006, where she and Sean Hayes recreated the iconic Annie Leibovitz photo of John Lennon and Yoko Ono:
7. Zoe Saldana posted these behind-the-scene photos taken on the set of her 2016 film, Star Trek Beyond:
Caption these… #FBF #BTS @StarTrek
8. Shania Twain posted these behind-the-scenes photos taken on the set of her 1999 music video for "Man! I Feel Like a Woman!":
9. Legendary rock photographer Mick Rock shared this classic photo he took of the Ramones in the '70s:
10. Dolly Parton posted this photo of herself looking pretty in pink in the '70s:
11. Justin Theroux shared this PETA PSA he recorded in 2010 to remind people to bring their pets indoors because of the polar vortex:
12. The Spice Girls shared this photo of themselves during their 1998 Spiceworld Tour:
13. And finally, Katharine McPhee posted this photo of herself and Meghan Markle, aka the Duchess of Sussex, in what appears to be the late '90s:
both did musicals together as a kid. one is now the duchess and the other is starring on the west end. basically the same life if you ask me #tbt