Telescopes designed for the observation of the X-ray sources in solar flares, i.e., bursts of radiations originating in the solar atmosphere, consist of pairs of tungsten grids located in front of high-energy detectors. Measurements of the intensity of the X-ray flux transmitted through the grids allow the computation of a very sparse sampling of the two-dimensional Fourier transform of the signal integrated along the line-of-sight [1]. Therefore, images of the two-dimensional distribution of the flaring X-ray sources on the solar disk can be reconstructed by solving an inverse problem from limited Fourier data [2]. Since October 2022, for the first time, two X-ray imagers have been simultaneously observing the Sun from different vantage points: the Spectrometer/Telescope for Imaging X-rays (STIX; [3]) on board the ESA Solar Orbiter spacecraft, and the Hard X-ray Imager (HXI; [4]) on board the Chinese ASO-S mission. In this talk, we describe how the datasets provided by the two telescopes can be combined to obtain a limited number of three-dimensional Fourier components of the flaring X-ray sources, and we discuss how combined datasets can be utilized to perform, for the first time, three-dimensional reconstructions of the flaring X-ray intensity. Further, we show how the singular values of the forward operator depend on the relative angle between the telescopes and the flaring site, and we characterize the degree of ill-posedness of the inverse problem. Finally, we present the results obtained from experimental data recorded by STIX and HXI on October 3rd 2024. [1] Massa, P., et al. The STIX Imaging Concept. Solar Physics (2023) 298(10):114. https://doi.org/10.1007/s11207-023-02205-7 [2] Piana, M., Emslie, A.G., Massone, A.M., and Dennis, B.R. Hard X-ray Imaging of Solar Flares. Springer Berlin (2022). http://dx.doi.org/10.1007/978-3-030-87277-9 [3] Krucker, S., et al. The Spectrometer/Telescope for Imaging X-rays (STIX). Astronomy & Astrophysics (2020) 642:A15. https://doi.org/10.1051/0004-6361/201937362 [4] Zhang, Z., et al. Hard X-ray Imager (HXI) onboard the ASO-S mission. Research in Astronomy and Astrophysics (2019) 19(11):160. https://dx.doi.org/10.1088/1674-4527/19/11/160