Rudy Giuliani, who served as mayor of New York City from 1994 to 2001, mourned the death of former New York City Police Department Commissioner Bernard “Bernie” Kerik on Thursday, describing the grief of losing his “best friend” and a “true patriot” as “inexpressible.”

Kerik died at 69 years old “after a private battle with illness,” according to FBI Director Kash Patel. 

Kerik and Giuliani were prominent figures during and after the Sept. 11, 2001, terrorist attacks in New York City due to their leadership roles in the city, and they quickly became close friends.

“On September 11th, Bernie Kerik and I saved each other’s lives. If we weren’t already friends, that bound us together forever. He was my best friend, a true Patriot, and one of the bravest men I’ve ever known,” Giuliani wrote in a statement.

Kerik’s 35-year career has been recognized with more than 100 awards for meritorious and heroic service, including a presidential commendation for heroism by President Ronald Reagan and two Distinguished Service Awards from the Department of Homeland Security.

He was considered for the role of Homeland Security chief in 2004, but lied to the White House during vetting, which ultimately led to him pleading guilty to eight felonies, including tax fraud, in 2009. He spent about three years in prison, then moved to home confinement and, later, supervised release.

President Donald Trump pardoned him of the convictions in 2020.

Kerik is survived by his wife, two daughters and one son, who is also a “brave and accomplished” police officer, Giuliani said. (Mireya Acierto/Getty Images)

Kerik worked with Giuliani again to investigate claims of election fraud following the 2020 presidential election.

Giuliani expressed his condolences to Kerik’s wife, his two daughters and his son – who is also a police officer – and said he believes all of Kerik’s friends and admirers are “much better for knowing him.”

Fox News Digital’s Sarah Rumpf-Whitten and Andrea Margolis contributed to this report.