"A year ago today my son Vance was diagnosed with cancer... he was 16 years old. He kept it very quiet... we all did," Billy wrote.
Over the past year, Vance went through 28 rounds of chemotherapy, however his proud dad said his son remained "positive, focused and kept his life as normal as possible... every single day."
Vance also celebrated the good news on his Instagram, writing, "Got diagnosed a year ago today, been clear for months now."
Billy wants the world to know that he couldn't be prouder of his "tough as nails" son.
"You don’t really understand human nature unless you know why a child on a merry-go-round will wave at his parents every time around - and why his parents will always wave back." - William D. Tammeus
"Heart of gold. Courage, strength, bravery, attitude, warrior... never seen anything like it," he wrote. "Never been prouder. Love you son."The "Northern Rescue" star also took the opportunity to give a shout out to everyone who helped support Vance over the past year, including his mother, two siblings, friends, teachers, coaches and the entire Santa Barbara, California community.
He saved the last word for his son's oncologist, Dr. Lawrence Piro, writing, "You are an amazing man!!"