Washington (CNN) Kay Hagan, a former US senator from North Carolina and the first female Democratic senator to represent the state, died Monday, her family said in a statement. She was 66.

"We are heartbroken to share that Kay left us unexpectedly this morning," the Hagan family said. "Kay meant everything to us, and we were honored to share her with the people of North Carolina whom she cared for and fought for so passionately as an elected official."

Hagan, a Democrat, served in the Senate from 2009 to 2015 after defeating Elizabeth Dole. She lost her reelection bid in November 2014 to Republican Sen. Thom Tillis. Tillis said in a tweet Monday that he was "heartbroken" by Hagan's passing and remembered her for her "dedicated and distinguished record of public service to our state & nation."

Hagan is survived by her husband, Chip Hagan, and children Jeanette Hagan, Tilden Hagan and Carrie Hagan Stewart. They remembered her "humor and spirit as the hub of our family" and said in their statement that she had a knack for making people feel welcome.

The family did not provide information on the cause of her death, but said they "are deeply grateful for the support shared with our family as Kay worked to regain her strength these last few years after her illness."

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