The contact of heterogeneous materials with different atomic structures and concentrations becomes omnipresent in modern materials. The differences across the interface introduce various gradients that could alter thermodynamic and kinetic behaviors of the materials. Here, we report a spontaneous melting of the interface formed by a crystalline metal and an amorphous solid at the temperature below their respective equilibrium melting temperatures. The transformation can even become continuous with disappearance of all known features of the first-order melting transition. We show that the change in the nature of melting in the interface region is caused by random disordering induced by interdiffusing atomic elements or impurities in the crystalline phase and the presence of a strong concentration gradient constrained by the sample geometry.