New Yorkers high and low mourned after hearing that the beloved newscaster John Slattery, a comforting and familiar face on WCBS-TV for 30 years, had died of an apparent heart attack Wednesday night at the age of 63.

"NYC has lost a great journalist," Mayor Bill de Blasio wrote on Twitter.

WCBS reporter Pablo Guzmán devoted the bulk of his Twitter feed to reminiscences about his colleague, who he described as a compassionat man of faith with little tolerance for religious hypocrites, and a journalist who "absolutely stood firm against attempts by police & "officials" to limit what you SHOULD know."

Guzmán also reprised the dapper Irish-American's famous sense of humor: Slattery purchased and erected a Puerto Rican flag at his desk when the two sat together, Guzmán recounted, "just to trap people who assumed the flag was mine."

Other colleagues added their own lamentations.

"We have lost our Shop Steward in more ways than one. Rest in Peace John Slattery, we miss you already," tweeted WCBS news anchor Chris Wragge, who also wrote that Slattery was the "gold standard" in news reporting.

Slattery will be waked Monday in Mamaroneck and his funeral is set for Tuesday in Larchmont. Arrangements are private. 

"Our thoughts and prayers are with John's wife, Suzie, and their children and grandchildren," WCBS/2 President and general manager Peter Dunn said in a statement.

A four-time Emmy winner who covered the 9/11 attacks, the "miracle on the Hudson" landing of US Airways Flight 1549, Superstorm Sandy, and the 1996 World Series, among other major stories, Slattery was prized for his distinguished and reliable reporting, yet down to earth and convivial communication style.

A Westchester resident, Slattery had also served as 2010 president and writer for The Inner Circle, a group of political reporters who raise money for charity by spoofing political figures in an annual show. He had performed as John Wayne Bobbitt, Pope Benedict, President George W. Bush and other notables, and "wasn't above going below the belt to get a laugh," especially if he felt that a public figure merited lampooning, said his friend Larry Sutton, an editor for books published by People magazine.

Slattery, "was a totally good guy. Most amazingly, he was able to keep a job at the same station for 30 years. That doesn't happen anymore," Sutton said.