PEOPLE.com) -- First Joni Richardson endured the death of her daughter-in-law, Diff'rent Strokes star Dana Plato, in 1999. Now almost exactly 11 years later, Plato's son, Tyler Lambert, committed suicide at the age of 25. "It's a shame that such a talented human being would do this with his life," Richardson told PEOPLE. "He had all the opportunities in the world and we just can't understand it." According to Richardson, her grandson, a cameraman and amateur songwriter, had long struggled with his mother's premature death at age 36.