AceShowbiz -

Robin Williams' oldest son Zak Williams remembered his late father at Christopher and Dana Reeve Foundation fundraising gala in New York recently. 31-year-old Zak broke silence on his dad's death for the first time, revealing how the family coped with his passing.

"It's tremendously sad ... we're trying to stay strong," he told PEOPLE. "The key thing that I want [people] to know is that we're doing okay." He went on, "We're experiencing the new normal now. It's tremendously sad. But healing is a long-term process. We've got a great group of people helping us through it."

Zak also told Entertainment Tonight at the same event, "A large part of what we're doing through this grieving process is giving and spending time focusing on others." He added, "The outpouring was remarkable. People shared their loving words, supportive words, art, and all sorts of amazing tributes to my father."

During the event to honor his late father and their friends, Christopher Reeve and his late wife Dana, Zak told the crowd, "In the spirit of honoring them, I need to ask of you two things. One: Tell the people you love that you love them at any and every opportunity. If they are in physical pain, tell them that there is hope. If they are in mental anguish, tell them there is hope. There is always hope."

"Two: Be a superhero. I challenge you to do good," he continued. "Time is precious and bringing light and healing where there is darkness, pain or suffering is absolutely vital."