BOSTON (CBS) – Family and friends are mourning the death of State Senator Ken Donnelly.

The senator’s office says the Arlington Democrat’s cause of death was a brain tumor he fought for eight months.

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He represented the 4th Middlesex District and was the Majority Whip and the Assistant Majority Leader. Donnelly was first elected to the State Senate in 2009.

His senate office said in a statement that Donnelly was dedicated to representing the voiceless.

“Throughout his career, he fought to save others, protect the most vulnerable in our society, and give voice to working men and women across the Commonwealth.  He was a staunch believer in the role of unions and government to protect workers, and he was well known for his efforts to advance justice and equality for all people no matter their race, religion, national origin, or sexual identification,” his office said.

Before running for office, he spent 35 years on the Lexington Fire Department and rose to the rank of Lieutenant.

He is survived by his wife Judy and his two sons Ryan and Keith, his daughter Brenna and five grandchildren.

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Details on his wake and funeral arrangements will be announced when available.