Action News confirmed the long-time educator entered hospice on Wednesday.
The Valley native led Fresno State for more than seven years.
He made history as the first California native and Mexican-American to become chancellor of the CSU system in 2021.
Dr. Castro resigned from that position a year later amid criticism of how he handled sexual misconduct allegations against a Fresno State administrator.
In 2023, he returned as a professor at Cal Poly San Luis Obispo but later announced his retirement due to serious health issues.
This week, friends and community members have been sending prayers and words of support to Castro's family on social media.