Rob Kim/Getty
Chelsea Clinton.
The vice-chair of the Clinton Foundation and only child of Bill and Hillary Clinton announced on Twitter that her daughter, Charlotte, would be a big sister next summer.
In the photo posted to Twitter, Charlotte was reading a book titled, "Big Sisters are the Best."
Clinton's husband is hedge fund manager Marc Mezvinsky. The couple's first child was born in September 2014.
Next summer, Charlotte is going to be a big sister! Feeling very blessed & grateful this holiday season. pic.twitter.com/gpCGqcmeCq
- Chelsea Clinton (@ChelseaClinton) December 21, 2015