Diamond is a promising material not only for electronics and quantum devices but also for radiation environments. Especially a single-crystal diamond has superior characteristics for high temperature, high frequency, high radiation, and high voltage applications. With the motivation of achieving non-invasive position and intensity measurements at 4.5 MHz for hard X-rays, the X-ray Photon Diagnostics group of the European X-ray Free-Electron Laser (XFEL) Facility initiated an R&D project on the development of diamond sensors. At very hard X-rays in particular the gas-based devices lose sensitivity and diamond-based sensors are a useful complement. A duo lateral diamond sensor was mounted on an XY motorized manipulator and attached to the K-monochromator vacuum chamber in SASE2 (Self-Amplified Spontaneous Emission) tunnel XTD1 (X-ray Tunnel for Distribution). The sensor consists of a single crystal CVD diamond produced by chemical vapor deposition. Both surfaces are covered by DLC-layers with defined resistivity, and on each side two planar metallized electrode strips allow collection of the generated currents. The dimensions of the sensor are 4 x 4 mm2 with a thickness of 40 μm. It is an electronic grade diamond with a charge collection efficiency of almost 100%. The first functional tests were performed at standard photon energies around 12-15 keV in July 2022 and further measurements were made at a particularly high photon energy of 30 keV which was exceptionally available during a facility development week at the end of November 2022. The preliminary results show that the diamond sensor delivers pulse-resolved beam position and intensity information at 2.25 MHz , and the results are in good agreement with measurements by adjacent monitors such as the FEL-imager and X-ray gas monitor (XGM).