In the snapshot, Hathaway looked red-carpet ready in a chic, shimmering burgundy gown with a pink clutch, while Moore, then 17, rocked a grey jacket over a black t-shirt and denim jeans.
"I guess this film came out just over 17 years ago??" Moore captioned the cute pic. "@annehathaway was already a movie star and I showed up to my first premiere in a casual denim suit. Hey, it was 2001! #tbt #theprincessdiaries"
"That's the face I make when I'm trying to not flop sweat on a terrifically famous pop star," Hathaway commented on the Instagram post, referring to Moore's successful career as a singer long before she started acting. "So happy for all that you have going on!"
In The Princess Diaries, Hathaway starred as Mia Thermopolis, a high school girl who discovers she actually the heir to the throne of a small European nation, ruled by her grandmother, played by Julie Andrews.
Meanwhile, Moore played Lana Thomas, one of Mia's chief antagonists at her school, who ends up getting her comeuppance when Mia plasters her with ice cream -- a scene Hathaway called back to in her comment.
"Let's get together and throw ice cream at each other soon," Hathaway suggested.
Moore was quick to respond with a lot of love for the idea of reuniting.
"Hello friend! Count me in. It'd be an honor to be coned by you again!" Moore replied, along with a laughing emoji and a heart.
The possibility of a Princess Diaries reunion excited quite a few fans of the film, including journalist and author Ronan Farrow who chimed in, "There aren't enough 'like' buttons in the world for this."
While a reunion doesn't necessarily mean there's another installment in the Princess Diaries franchise anytime soon, the possibility of making the series a trilogy has long been an idea floating around among the films stars.