  We present an analysis of a flare on the Wolf 359 star based on simultaneous
observations of TESS and XMM-Newton. A stellar flare with energy comparable to
an X-class solar flare is analyzed on this star for the first time. The main
goal of the study was to determine whether the same physical processes drive
and occur in stellar flares as in the solar flares. We tried to estimate the
flare class by various direct and indirect methods. Light curves and spectra in
different energy ranges were used to determine the parameters and profiles of
the flare. From the XMM-Newton EPIC-pn X-ray data, we estimated the temperature
and emission measure during the flare. The thermodynamical timescale and the
loop semi-length were also determined with two different methods. The RGS
spectra enabled us to calculate the differential emission measure (DEM)
distributions. The obtained DEM distributions have three components at
temperature values of 3 MK, 7 MK, and 16-17 MK. The analysis of the line ratio
in helium-like triplets allowed us to determine the plasma electron density.
Our results for the flare loop on Wolf 359 were compared to typical parameters
for solar flares observed with GOES and RHESSI. This supports our conclusion
that the processes taking place in stellar flares are like those in solar
flares. The determined geometrical parameters of the phenomenon do not differ
from the values of analogs occurring on the Sun.
