X-ray free electron lasers (XFELs) provide 10–100 fs long pulses containing 10¹²–10¹³ photons in the 5–15 keV photon energy range. Although such a pulse contains comparable number of photons to those that are used in hours-long single crystal diffraction experiments, the conventional experimental techniques are not suitable for measurements using a single XFEL pulse. To determine the 3D atomic structure of crystalline materials using a single XFEL pulse, new measurement techniques must be developed. X-ray fluorescent atoms within a crystalline structure, used as secondary X-ray sources for diffraction result in Kossel lines instead of Bragg reflections. In this talk I will explain what the fundamental differences are and why it is necessary to change from Bragg reflections to Kossel lines in an ultrashort single-pulse diffraction measurement. I will describe the experimental details, show the steps of structure solution and the results of our demonstration experiment performed at the European XFEL [Nature Communications (2024) 15:970.].