Neil Winter, the mayor of Menifee, died at his house overnight, the city announced Sunday.
And state Assembly member Melissa Melendez said that firefighters were rushed to his house Saturday night and found him in full cardiac arrest.
Winter, 65, was a political newcomer when he was first elected mayor in November 2016. He was only the third mayor since the city's incorporation in 2008.
Running a grassroots campaign, he beat out incumbent Scott Mann, whose campaign was hit with a $60,000 fine from the California Fair Political Practices Commission for campaign finance violations.
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"Neil changed the culture of the city and worked tirelessly to connect with the residents," Menifee Union School District Trustee Jerry Bowman said in a Facebook post.
The city's statement said that more details will be released in the days to come.
Menifee Third District Councilwoman Lesa Sobek is the city's Mayor Pro Tem and will take on mayoral responsibilities, in the absence of the mayor.