"Today was a VERY IMPORTANT day for me," Portman wrote on Instagram. "I read every single book of the Babysitter's Club when I was a child. Once, when I was 9, I waited in line for hours in my local library to meet Ann M. Martin. And today I received this by mail from her."
The "BSC" book that was sent to her is "Kristy and the Walking Disaster" from 1989, in which Kristy Krushers, a softball team, faces a big game, while Kristy takes care of a crush.
Portman wrote of the story: "I'm so lucky that I grew up with books about girls who worked together, supported each other, were entrepreneurs and they all had very different personalities. I still identify myself as a Kristy mixed with Stacey and a pinch of Dawn. Which baby-sitter are you? "
As for his inscription, Martin wrote: "For Natalie Portman – BSC 4 of all time! With admiration, Ann M. Martin."