Fernando Richter, the man who kept his 3 daughters imprisoned for years, was assaulted in prison, according to the Arizona Department of Corrections.
Officials say two inmates beat him and he suffered non-life threatening injuries.
He was sent to the hospital, but will be okay.
Last year, a judge sentenced Richter to 58 years in prison.
He will be in his 90s when he is released.
His daughters said Richter locked them in their bedrooms, monitored them with a camera, and only fed them twice a day.
The food was a mixture of pasta and scraps.
The mother, Sophia Richter, may also be involved in this case.
She was first sentenced to 20 years in prison, but was recently granted a new trial.
The court will determine if she only acted on her Fernando's behalf out of fear for her life.