Jenna Bush Hager Says She 'Witnessed in Awe' as Her 'Toughest' Twin Sister Barbara Became a Mom

Jamie McCarthy/Getty Jenna Bush Hager (left) and Barbara Pierce Bush

Jenna Bush Hager is congratulating twin sister Barbara Bush on becoming a mother.

Their parents, former President George W. Bush and former First Lady Laura Bush, announced in a statement Tuesday that Barbara, 39, gave birth to her first baby, daughter Cora Georgia, with husband Craig Coyne on Monday, Sept. 27.

"With full hearts, Laura and I are delighted to announce the birth of our new granddaughter," read the statement. They added, "Cora is healthy and adorable, and we are proud and grateful."

Jenna — who shares kids Margaret "Mila" Laura, 8; Poppy Louise, 6; and Henry "Hal" Harold, 2; with husband Henry Hager — celebrated the news on Instagram, writing: "Dearest Cora Georgia, Today is the day I got to meet my most beautiful, precious, feisty, niece (a bit earlier than we expected!)"

"I witnessed in awe as my dearest, toughest @barbara.p.bush became a mama," she continued alongside a series of photos from the hospital. "And today is the day I fell in love! Some cousins are anxiously waiting to play with you, but not just yet love. Xx auntie j"

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In an interview with PEOPLE ahead of this year's George H.W. Bush Points of Light Awards, Barbara said one of the "silver linings" of the pandemic was being able to stay with her parents at their Texas ranch.

"When we went to stay with my parents, we thought it would be for a handful of weeks — we didn't anticipate that it would be for the majority of a year," Barbara said. "But it's time that we never otherwise would've had, of course."

"There's something really lovely about the simplicity of being with someone every day, rather than when we normally are with our family where it's around the holidays or it's for this very condensed amount of time," she added.

On their birthday last November, Jenna honored Barbara on Instagram, writing at the time, "Happy birthday to my partner since birth. I don't know life without this beautiful, giving gorgeous soul — and wouldn't want to. I'm the luckiest to be born walking through life side-by-side with the small girl with the largest heart. I adore you @barbaritabush!"

Jamie McCarthy/Getty From left: Craig Coyne and Barbara Pierce Bush

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Last year, Jenna wrote in her book Everything Beautiful in Its Time: Seasons of Love and Loss about becoming pregnant with son Hal, sharing that she felt nervous to tell her newlywed sister about the news. She wrote that even her parents were worried about her sister's response to the pregnancy at the time.

"They were delighted, but the first thing my father said was, 'Have you told Barbara?' I knew my father was worried that Barbara, newly married, would likely be trying soon for a baby if she wasn't already," Jenna wrote. "My parents went through so much in order to conceive us, so they are sensitive to the feelings of anyone who does not yet have the babies they want. They thought that if Barbara was trying, she might understandably envy my pregnancy."

"My mother scolded my father for putting that pressure on me," she added. "She said what she always says when these questions arise: 'Every woman gets her baby in her time.' "

Jenna explained to them, however, that she had already told Barbara, who had laughed at the news, saying, "Three kids? Holy s---!" before congratulating her.