The advent of X-ray free-electron lasers, delivering ultra intense femtosecond X-ray flashes, opens the door for structure determination of single nanoparticles and biosamples with single shots. The first X-ray diffraction imaging experiments at LCLS were successfully performed on mesoscale single viruses and nanocrystals delivering promising results. However, the reconstruction of non-periodic structures from coherent X-ray diffraction pattern is still challenging due to the loss of phase information. Meanwhile, X-ray holographic approaches allow for recording the phase directly into the diffraction image. While well established for fixed targets, X-ray holography in the gas phase still remains a great challenge. In my talk, I will present the first successful proof-of-principle experiment for "in-flight"-holography with unsupported viruses. Here, Xe clusters act as reference scatterers in a gas phase holographic setup. The promising results pave the way for unique studies on non-cristalin nanospecimen that are of central interest in several scientific communities including atmosphere research, chemistry, material sciences, and studies on matter under extreme conditions.