Device-to-Device (D2D) communication is one of the promising and revolutionary technologies in 5G cellular networks that enables mobile terminals to communicate directly without the base station involvement. One of the major objectives of 5G for this paradigm is to provide seamless mobility satisfying QoS requirements. Hence, the handover process between various radio cells is an important issue faced by D2D candidates. This paper presents a new analytical model in order to evaluate the handover performance of the D2D pair operating with the practical Reference Point Group Mobility (RPGM) mobility model. Such a system is modeled as a two-stage open network and a multidimensional Markov Chain to compute performance metrics, such as blocking probability of originating D2D calls, handover failure probability or missing and unnecessary handovers rate. General formulas are given and numerical results evaluating the system performance are presented.