Luminous Blue Variables (LBVs) are massive stars caught in a post-main sequence phase, during which they are losing a significant amount of mass. Given the potential importance in its evolution of the binary nature of the most dramatic example of the class, eta Car, and the fact that most massive stars are thought to be close binaries, it would be useful to find other binary LBVs. We present here interferometric observations of the LBV HR Car done with the AMBER and PIONIER instruments and ESO's Very Large Telescope Interferometer. Our observations, spanning two years, clearly reveal that HR Car is a binary star and we have detected the orbital motion, leading to an orbital period between 5 and 80 years. Our results show that the LBV HR Car is possibly another eta Car-like binary system, showing possible signs of interaction at periastron and further monitoring of this object will clearly constraint the orbit and the total mass of the system.