Rep. Sean Casten (D-Ill.) on Monday evening announced that his daughter, Gwen Casten, had died.

“This morning, Congressman Casten’s beloved daughter, Gwen (17), passed away. The Casten family requests privacy, and we will be issuing no further comment during this heartbreaking time,” Casten tweeted.

The cause of his daughter’s death was not immediately clear.

Downers Grove police responded to a complaint about "an unresponsive 17-year-old female" early Monday morning on the Illinois Democrat's street, according to the Chicago Tribune. "First responders found the victim was deceased," the statement read.

Casten was among the House members who voted to pass legislation last week that would nationalize red flag laws.

Gwen Casten’s Twitter bio also indicates she was involved gun-violence advocacy work as a March for Our Lives co-director for their Illinois chapter.

She had recently been featured in a campaign ad for the lawmaker as he seeks a third term in Congress.

Hughes ran against Newman in 2020 in Illinois' 3rd Congressional District but finished fourth with 2.3% of the vote.