The Moon River crooner lost his battle with cancer at the age of 84, and stars including Robbie Williams, Reba MCEntire, Josh Groban and Osmond's sister Marie have already offered up tributes to the star.
Now, the Puppy Love hitmaker has paid his own respects to Williams, who toured with Osmond and his singing siblings at the beginning of their careers and welcomed them onto his top-rated TV specials.
Osmond reveals he was "always impressed" by Williams' stage presence and will "treasure" the singing lessons his mentor gave him when he was starting out.
In a post on his website, he writes, "Andy Williams was an inspiring man in both his music and his life. The clarity and warmth and grace of his singing shaped my love of music as I watched my brothers perform with him on his weekly show.
"When I finally joined my brothers and toured with Andy as his opening act and back-up singers, I was always impressed with the way he handled an audience. He loved the audience. That was one of the most important lessons he taught me.
"The best way I could describe his voice was 'pure'. It was always pleasant to listen to. I will always treasure the memories of when I was 7 years old and he took the time to give me several voice lessons. He truly was a great singer and I will ever be indebted to Andy for giving me the opportunity to fulfil my dreams and the opportunity to be personally inspired by such a generous talent."