The formation and melting of a mono-layered charged dust particle crystal in a DC glow discharge Argon plasma is studied. The nature of the melting/formation process is established as a first order phase transition from the nature of the variations in the Coulomb coupling parameter, the dust temperature, the structural order parameter and from the existence of a hysteresis behavior. Our experimental results are distinctly different from existing theoretical predictions for 2D crystals based on the KTHNY mechanism or the Grain boundary induced melting and indicate a novel mechanism that is akin to a fluctuation induced first order phase transition that has not been observed before in complex plasmas. PACS numbers: 52.27.Lw, 52.35.Fp, 52.35.Sb Introduction.-The phase behaviour of two dimensional structures, particularly the nature of their melting transition, has long been a subject of theoretical and experimental interest and also the source of some controversy. Some commonly studied two dimensional structures are molecular monolayers formed by surfactants spread on a water layer [1], electrons on the surface of liquid Helium [2], colloidal suspensions of charged sub-micron spheres [3] and more recently single layer crystalline structures of charged micro-particles (dust) suspended in the electric sheath of a plasma [4][5][6][7]. Two dimensional structures have also been the subject of many computer simulations based on simple theoretical model systems [8][9][10][11]. The most well known theory for two dimensional melting is the one proposed by KTHNY [12] which describes the melting as a two stage transition process with an intermediate hexatic phase. The melting begins by forming dislocations and disclinations in the 2D crystalline structure and as a result the long range translational order breaks down and leads to a hexatic phase. The transitions from the solid to the hexatic and then on to the liquid phase are both continuous in nature constituting second order transitions. Other competing mechanisms of melting consist of the Grain-boundary induced (GBI) melting theory [13,14], the density wave theory [15] and the instability triggered theory [16]. The GBI melting [13,14] proceeds through long arrays of dislocations at the lattice boundaries that drive a first order phase transition from the crystalline phase directly to the liquid phase. Density wave theory [15] deals with the change of entropy and structure factor variations, but it fails to establish the order of the phase transition. Likewise simulation studies to date do not provide a definitive picture of the nature of the 2D melting phase transition and the question still remains open.The advent of dusty plasma crystals in recent times has provided a strong impetus to the experimental study of 2D melting since the process can be well diagnosed using non-perturbative techniques and a number of such studies have addressed this problem [4,6,7,[17][18][19]. In