The Multipath Transport Control Protocol (MPTCP) is undergoing a rapid deployment after a recent and quick standardization. MPTCP allows a network node to use multiple network interfaces and IP paths concurrently, which can lead to several advantages for the user in terms of performance and reliability. In this paper, we describe an MPTCP implementation in the Network Simulator 3 (ns3), comparing it with both the Linux implementation and previous ns3 implementations. We show that it is compatible with the Linux implementation and that it has a desirable similar behavior in traffic handling. Our goal is to allow researchers develop and evaluate new features of MPTCP using our simulator in a much faster way than they would with a kernel implementation, hence boosting MPTCP research.