At the time, the 15-year-old (15!) had a hit with her single "Candy." She later had hits with 2000's "I Wanna Be With You" and 2001's "In My Pocket." She's still singing as Rebecca on the NBC series "This is Us."
On her Instagram post, she wrote: "Summer of 1999. Abercrombie tshirts and bucket hats. Opening for this guy and his band. Look at my nervous smile! 🙈 #tbt #memories"
And as for what her "This is Us" hubby Milo Ventimiglia was doing in 1999, remember a little movie called "She's All That"? He appeared in the romcom as "Soccer Player" who shows up to help clean Rachael Leigh Cook's house.