Zak Williams is "still grieving".
The 32-year-old tech marketing executive - whose father Robin Williams died last August - has revealed his family are still struggling to come to terms with the death of the 'Mrs. Doubtfire' actor.
He said: "We try to focus on the joyful moments and memories.
"We're still grieving. We're moving through the process of healing and recovering."
Zak celebrated what would have been his father's 64th birthday on Tuesday (21.07.15) along with his siblings Zelda, 25, and Cody, 23, as well as other relatives by having a private dinner, and said they have been helped by "wonderful family and friends" during the 11 months since Robin's passing.
And to honour his dad's life, Zak revealed he has been following in his footsteps by volunteering at San Quentin State Prison teaching financial literacy with a nine-month program which has helped him with his "healing" process.
He told People magazine: "As I go through the process of healing, working with inmates and focusing on the Financial Literacy Initiative and criminal justice reform has been healing for me."
However, the Williams family are still believed to be embroiled in a bitter dispute over how to divide the late star's fortune as while Robin's widow Susan claims her husband's trust was "ambiguous", Zak, Zelda and Cody insist he wanted his children to become the rightful owners of his personal items.