9-year-old Oklahoma boy breaks down in 'happiest tears ever' as he finishes chemotherapy

NORMAN, Okla. -- A 9-year-old Oklahoma boy broke down in tears of joy while taking his final dose of chemotherapy medication, capping off a three-year battle with cancer that he fought "with a smile on his face and his head held high," according to his mother.

Ashley Cotter posted the emotional video of her son, Steven, to Facebook over the weekend. The video she posted had no sound, but -- she said -- "you can just feel" the "pure happiness" of the moment, which she said was "one of the most proud moments I've ever lived!"

In it, a visibly emotional Steven takes his final round of chemotherapy drugs before joining his father in a warm embrace as his younger brother and friend cheer for him across the room.

Steven was diagnosed with high-risk acute lymphoblastic leukemia in August 2016 when he was just six years old, his mother told ABC. He underwent his first chemotherapy treatment just days later, treatments that continued every day until this past weekend.

"He's had so many blood and platelet transfusions over the past three years, so many medications and hospital stays," his mother recalled.

She followed up with a second Facebook post showing Steven next to a table full of dozens of pill bottles, which she said was "just a touch of what he's had to take" over the course of his treatment.

Though she described the experience as "heart-wrenching" and said it was "absolutely horrible to hear the words 'your son has cancer,'" Cotter said she and her family "have come so much closer as a family, came closer to God and always kept the faith!!"