The first person believed to be cured of HIV has died, BBC reported Wednesday. Timothy Ray Brown, also known as the “Berlin patient,” was diagnosed with leukemia in 2007 and had a bone marrow transplant from a donor who had the rare CCR5 gene mutation, which essentially blocks HIV. Brown’s HIV levels dropped to the point the virus became virtually undetectable and he no longer needed anti-retroviral medication, effectively rendering him cured. However, the leukemia returned earlier this year and spread to his brain and spinal cord.

“Tim committed his life’s work to telling his story about his HIV cure and became an ambassador of hope,” said his partner Tim Hoeffgen on Facebook. In his later years, Brown got involved in HIV awareness and prevention activism, publicizing his identity as the Berlin patient and advocating for pre-exposure prophylactic HIV therapy and “U=U,” or undetectable means un-transmissible, a finding about HIV positive patients supported by the CDC.