In this paper, we consider a cooperative network comprising of a source node, a destination node and M amplifyand- forward half-duplex relay nodes. Both the source and destination have one antenna and each relay is equipped with N antennas. There exists a buffer at each relay in order to store the incoming data packet and retransmit it to the destination later. At each time slot, simultaneous data transmission of the source and one of the relay results in inter-relay interference (IRI). We propose a novel buffer-aided relay selection scheme which mitigates the IRI with the aid of minimum variance (MV) beamforming and the relay buffers. More specifically, at each time slot, two relays are selected to receive data from the source and to transmit data to the destination provided that the associated source-to-destination signal-to-interference-plus-noise ratio (SINR) is maximized. By simulations, we investigate the performance of the proposed policy in terms of the throughput, delay, outage probability and SER (symbol error rate). It is shown that the proposed scheme suppresses the IRI efficiently, achieves higher throughput and lower outage probability compared to the other recently proposed successive relaying policies.