  We present the first detection of solar flare emission at middle-ultraviolet
wavelengths around 2000 A by the channel 2 of the Large-Yield RAdiometer (LYRA)
onboard the PROBA2 mission. The flare (SOL20170906) was also observed in the
channel 1 of LYRA centered at the H I Lyman-{\alpha} line at 1216 A, showing a
clear non-thermal profile in both channels. The flare radiation in channel 2 is
consistent with the hydrogen Balmer continuum emission produced by an optically
thin chromospheric slab heated up to 10000 K. Simultaneous observations in
channels 1 and 2 allow the separation of the line emission (primarily from the
Lyman-{\alpha} line) from the Balmer continuum emission. Together with the
recent detection of the Balmer continuum emission in the near-ultraviolet by
IRIS, the LYRA observations strengthen the interpretation of broadband flare
emission as the hydrogen recombination continua originating in the
chromosphere.
