"Your legacy lives on in your family and in those who carry your spirit within their hearts," Robin Williams' son Zak wrote on Instagram
Robin Williams, Zak Williams
Robin and Zak Williams
| Credit: Jamie McCarthy/WireImage

Robin Williams' eldest son Zak is paying tribute to his late father six years after the actor's tragic death.

Zak — whose mom is Robin's first wife, Valerie Velardi — posted a heartfelt message to Instagram on Tuesday, which marked exactly six years since his dad died at age 63.

"Dad, today marks six years since your passing," Zak wrote alongside a black-and-white photo of his father. "Your legacy lives on in your family and in those who carry your spirit within their hearts."

"We will continue to fight for what’s good in the world, for peace, and for connecting people instead of tearing them apart," he added. "Love you so much!"

Robin died by suicide on Aug. 11, 2014, after suffering from Lewy Body Dementia, a type of brain disease that affected his thinking, memory and movement control.

In May, Zak — who is on the Advisory Board of the mental health program, Inseparable— told PEOPLE that his 1-year-old son McLaurin Clement, who goes by Mickey, has been getting slowly introduced to the late entertainer.

"His mom [Olivia June] and I have certainly considered how we want to introduce my son's grandfather, my dad, into his life," said Zak "Certainly through his movies and the cartoons that he participated in is a great way. My son, Mickey, points at a cel that we have in his room of my dad that has the genie from Aladdin."

Zak added, "We hope that we can celebrate the positive elements and his works and films in a way that there can be appreciation and acknowledgment of him both as an entertainer, but also as a family man, and parent and grandfather to my son."

Zak Williams Alex Mallick baby
Zak Williams and family

Zak's heartfelt tribute to Robin came as his half-sister, Zelda, also honored their late dad. In her own Instagram post, Zelda, 31, said she would taking a break from social media on her father's death anniversary as she does every year.

"It's hard for me on regular, good day to remain the person expected to graciously accept the world's need to share their memories of him and express their condolences for his loss," Zelda said. "As I've said in the past, while I am constantly touched by all your boundless continued love for him, some days it can feel a bit like being seen as a roadside memorial — a place, not a person — where people drive past and leave their sentiments to then go about their days comforted their love for him was witnessed."

"But sometimes," the actress added, "that leaves me emotionally buried under a pile of others' memories instead of my own. After all, even roses by the truckload still weigh a ton."

Zelda and Robin Williams
| Credit: Zelda Williams/Instagram

In several follow-up tweets, Zelda shared resources, including the telephone number for the National Suicide Prevention Lifeline, for anyone coming to her Twitter page "in crisis" on Tuesday.

"Whoever out there needs to hear it, please use this as your signpost in the desert," she wrote, adding, "Reach out. Seek help. Keep fighting."

If you or someone you know is considering suicide, please contact the National Suicide Prevention Lifeline at 1-800-273-TALK (8255), text "STRENGTH" to the Crisis Text Line at 741-741 or go tosuicidepreventionlifeline.org.