Gary Sinise’s son has died following a rare form of cancer diagnosis. He was 33.

The 68-year-old Forrest Gump star announced the death of his son, Mac Sinise, in a post shared on the Gary Sinise Foundation’s website alongside a string of photos of them together.

In a message that has only now come to light, Gary said Mac – born McCanna Anthony – had passed away on January 5, due to spinal cancer Chordoma.

“I was always happy to have him join me on the road, and I could see how much joy and pride he shared in our mission. Especially when he could be hands-on with those we serve, like at our Soaring Valor events honoring our nation’s WWII heroes, and our Invincible Spirit Festivals, where we bring the Lt. Dan Band to uplift our wounded at military hospitals across the country,” the CSI: NY actor said about his son.

“Mac had been playing drums since he was nine years old and was an exceptional drummer. He would substitute for my drummer, Danny Gottlieb, when Danny was unavailable to play our Lt. Dan Band shows. Those were some great times, father and son rockin’ out together for the troops,” he wrote.

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Gary added that his family was struck by a double tragedy in the summer of 2018, when, in the space of three months, they found out his wife Moira had stage 3 breast cancer and then Mac had cancer.

Moira’s disease went into remission after successful surgery to remove lymph nodes, followed by chemotherapy.

Gary added in his post Chordoma is a “one in a million” form of cancer that affects, on average, only 300 people in the US per year.

“I am so blessed, fortunate, and proud to be his dad. We were blessed to have you in our lives as son, brother, and friend… and we will miss you and love you for eternity,” he concluded his post.