Illinois Rep. Sean Casten's 17-year-old daughter, Gwen, died Monday morning, his office confirmed.
In a short statement shared on Twitter on Monday night, his office said the lawmaker's "beloved daughter, Gwen (17) passed away."
"The Casten family requests privacy, and we will be issuing no further comment during this heartbreaking time," it said.
Casten's office did not provide any details on the cause of death.
The teenager had recently appeared in a campaign video supporting her father's bid for a third term in Congress.
In the video, released earlier this month, she spoke of how turning 18 would be a “big year” filled with “lots of milestones,” including “voting for the first time. But not just for anyone.”
"Sean Casten. My congressman. But I just call him dad," she said in the video, in which she championed her father's efforts on new gun laws and and protecting abortion access.
Casten, a Democrat, represents Illinois’ 6th Congressional District. He was first elected in 2018 and was the first Democrat to represent the district in nearly 50 years, according to his campaign website.
Tributes and words of support poured in for Casten's family in response to his office's announcement.
"This is awful beyond words," Illinois state Rep. Bob Morgan wrote in a tweet. "You and your family are in my prayers, and I hope you find strength in the difficult days ahead. May Gwen’s memory be a blessing upon us all."
"I am so very sorry. Sending you love and light," Illinois Lt. Gov. Juliana Stratton said.
Courtney DeMent, principal of North High School in Downers Grove, Illinois, asked students and families to keep Casten’s family in their thoughts.
“Our school community is grieving from the loss of 2022 graduate Gwen Casten, a shining star,” DeMent said in a written statement. “Many people are hurting right now and we send our love to the Casten family.”