"A Difficult Day that turned into a Beautiful Night…," Nick wrote June 24 alongside a picture of himself and friends on a beach next to huge blocks that spelled out Zen. "We will forever celebrate Zen's Light! I love you Son."
In a follow up Instagram Story, the 42-year-old wrote, "Happy Birthday Zen. We Love You Son..."
Alyssa also shared a message to Zen, who passed away from brain cancer in December 2021, on her own social media page.
"Happy heavenly birthday Zen," she captioned a black and white snap of the two in the hospital the day he was born. "When I get present enough, when I do what feels honest and true.. Somehow the moment leads me right to you. Me and the girls were able to see you in so many ways today.We love you for eternity. 6/23."
Since their son's death at 5 months old, Nick and Alyssa—who are also parents to daughter Halo, 6 months, have opened up about their grief.
"I always try my best to remain positive but right now I can't help but cry out "it's not suppose to be like this," the model wrote on Instagram June 2022 to mark what would've been Zen's first birthday. "In my mind I can see him smashing his cake and crawling around, tugging at my legs. But the reality is I will be the one to blow out his first candle. I will be wishing he was still here with us. GO REST HIGH."
Back in December, Nick shared some of the reasons why Zen did not go through with chemotherapy after doctors offered it.
"They pretty much told me that best case scenario, your son could live to 3 or 4 years old," he recalled on The Checkup with Dr. David Agus, per People. "So instantly when I heard that, I thought, quality of life. I wanted him to have the best existence he could have."
Having undergone chemo himself to treat lupus, Nick didn't want that for his son.
"Seeing your son hooked up to all of those machines—and he had to go for a shunt two or three times, and that was heartbreaking every time—even in that short amount of time, I couldn't imagine him having to go through chemo," Nick continued. "I knew how as a full grown man, that process. I wouldn't even call it pain. It just sucked everything out of you. I couldn't imagine that on a newborn and what that would do."
Nick is also dad to twins Moroccan Cannon and Monroe Cannon, 11, with Mariah Carey as well as Golden Cannon, 6, Rise Messiah Cannon, 8 months and daughter Powerful Queen Cannon, 2, with Brittany Bell.
He and Selling Sunset's Bre Tiesi are parents to son Legendary Love Cannon, 12 months, while he shares 9-month-old Onyx Ice Cole Cannon with LaNisha Cole. And he and Abby De La Rosa have three kids together, 2-year-old twin sons Zion Mixolydian Cannon and Zillion Heir Cannon and daughter Beautiful Zeppelin Cannon, 7 months.