Zak also reveals in a new interview that the Oscar-winning comedian's misdiagnosis with Parkinson's disease before his death really took a toll on him, making him uncomfortable and frustrated.

• Jul 22, 2021

AceShowbiz - Robin Williams will always be remembered by his family, closest friends and fans. On Wednesday, July 21, the late actor's son Zachary or Zak took to social media to share a heartfelt message on what would have been his 70th birthday.

Alongside a picture of the "Good Will Hunting" actor, Zak wrote in an Instagram post, "Dad, on what would be your 70th birthday, I would want you to know that your incredible spirit lives within us." He went on to say, "Our family will be celebrating you and your memory today. We miss you and love you always!"

Fans quickly sent love to Robin as well as his family in the comment section. "Sending you [heart emoji] and healing, and hope! We will always miss him. #WeAreWithYou and yours today Zak!" a follower commented. "Happy Birthday to Robin, the most amazing role model and actor, forever my favorite," a fan said. Another fan raved, "he is an incredible person that we will never forget, he will always remain in our memories and in our hearts!"

Someone else also chimed in, "Celebrating the heart brilliance and wisdom, the talent, gift, work and presence of your Dad - all of which endures." One other fan added, "Happy Heavenly Birthday Robin. Heaven is a lot funnier for sure!"

Robin died by suicide on August 11, 2014. Prior to his death, the Oscar-winning actor was incorrectly diagnosed with Parkinson's disease. Autopsy results revealed that the "Dead Poet Society" actor actually suffered Lewy Body Dementia.

In an interview with PEOPLE on his 70th birthday, Zak told host Max Lugavere on his "The Genius Life" podcast that the misdiagnosis took a toll on his father. "What I saw was frustration," Zak said. "What he was going through didn't match one to one [with what] many Parkinson's patients experience. So, I think that was hard for him."

Zak, who is a mental health advocate, added, "There was a focus issue that frustrated him, there were issues associated with how he felt and also from a neurological perspective he didn't feel great. He was very uncomfortable." He also noted that the medications "are no joke" and they were "really hard on the mind and the body."

"I couldn't help but feel beyond empathy. I couldn't help but feel frustrated for him. It can be really isolating even when you're with family and loved ones," Zak shared. His dad's death also affected his own mental health as he shared, "I was heavily drinking to manage my mental health where it created very harmful issues. For me personally, I was having health issues. I was experiencing some psychosis and when I spoke with a psychiatrist I was diagnosed with Post Traumatic Stress Disorder. I was self-medicating through the trauma using alcohol."