The 31-year-old Girls creator and star threw her support behind Jenner on Friday night, hours after news broke that Jenner was pregnant with her first child.
“A solid 10 friends texted me triggered by Kylie pregnancy,” Dunham tweeted on Friday night, explaining that her friends felt jealous that the 20-year-old Keeping Up with the Kardashians star was expecting her first child before they were.
“I’m like, ‘Ladies she’s 20. We were all [very] fertile then, we were just broke,’ ” Dunham joked.
She added: “You know the fertility industrial complex has pushed us too far when we’re trying to stay neck in neck [with] reality stars who can’t drink yet.”
“They started telling friends a few weeks ago,” said the source of the Keeping Up with the Kardashians star and her rapper boyfriend. “The family has known for quite some time. She is really excited and so is Travis.”
Another source close to the family told PEOPLE: “It is an unexpected but completely amazing turn of events that she could not be more excited or thrilled about.”
“Everyone is overjoyed for her,” the source said. “This is the happiest she’s ever been.”
RELATED VIDEO: Kylie Jenner, 20, Pregnant with First Child with Travis Scott: They’re ‘Really Excited,’ Says Source
Another insider said Scott began telling friends about the pregnancy in July. “He was so excited he couldn’t keep it in,” says the insider. “He’s been so affectionate and protective of Kylie since they found out. He can’t wait to be a dad.”
The source added Jenner was worried people would find out she was pregnant before she was ready to share the news, so she “started posting old photos of herself on social media” that flaunted her flat stomach.
“Kylie was really surprised but is so happy,” said the insider. “She wants to be a mom.”
Reps did not respond to PEOPLE’s request for comment.
Meanwhile, Dunham is birthing something else herself right now — a new television show with Girls showrunner Jenni Konner.
On Sept. 15, the two revealed they were hard at work on a new series while celebrating the second anniversary of Lenny Letter — the online publication they founded together — at a cocktail party co-hosted by Cole Haan at the Jane Hotel in New York City.
Since Girls aired its series finale in April, Dunham and Konner admitted it was weird to not be working on a new season of their acclaimed HBO show for the first time in 6 years — but that the new project was helping.
“It has been weird and kind of hard to get out of bed, but Lenny helps us through that and we’re now working on a new show” Konner, 46, told reporters.
“We’re back in business,” Dunham added.