Jenna Bush Hager, left, and Barbara Pierce Bush attend a luncheon on Jan. 25 in New York City. (Jamie McCarthy/Getty Images for The Hudson River Park Friends Playground Committee)

The 37-year-old Bush twins, once best known for sticking their tongues out at flashing cameras and partying in Georgetown, are writing a children’s book.

Jenna Bush Hager announced the news on NBC’s “Today,” the morning news program where she’s been a mainstay for the last decade.

“It’s all about sisterhood, whether its blood sisters like Barbara and me or friends or colleagues like y’all [who] can make your life better than you ever thought possible or make you braver,” Hager explained to her co-hosts Tuesday morning.

The picture book — titled “Sisters First,” the same name of the former first daughters’ memoir — follows a young girl and her new baby sister as the duo go through life together and make one another better. On its cover are two little girls who bear a striking resemblance to Hager’s daughters, Mila, 5, and Poppy, 3.

This is the third children’s book for Hager, who previously wrote a pair of books with her mother, former first lady Laura Bush.