The classical Poincaré conjecture that every homotopy 3-sphere is diffeomorphic to the 3-sphere is proved by G. Perelman by solving Thurston's program on geometrizations of 3-manifolds. A new confirmation of this conjecture is given by combining R. H. Bing's result on this conjecture with Smooth Unknotting Conjecutre for an S 2 -knot and Smooth 4D Poincaré Conjecture.