The son of Chicago Police Superintendent Eddie Johnson—Daniel Johnson—has been sworn in as a police officer a year after he donated a kidney to his dad, according to Fox News.

Superintendent Johnson said that the swearing in ceremony was “one of the most special days” of his life.

During the ceremony, Superintendent Johnson told the crowd of new officers and their families that he was on stage because of his son’s selflessness in donating a kidney. The elder Johnson had acute inflammation of the kidney and got a transplant in 2017.