Rudy Giuliani, the former New York City mayor and longtime ally of President Donald Trump, has been hospitalized in critical but stable condition, his spokesman said Sunday.

Ted Goodman, Giuliani’s spokesman, did not disclose what led to the hospitalization, how long Giuliani has been in the hospital or his prognosis. Giuliani is 81.

“Mayor Giuliani is a fighter,” Goodman said, adding that he was facing the health crisis “with unwavering strength.”