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Gaia21bty, a pre-main sequence star that previously had shown aperiodic dipsin its light curve, underwent a considerable $\Delta G\approx2.9$ magbrightening that occurred over a few months between 2020 October - 2021February. The Gaia lightcurve shows that the star remained near maximumbrightness for about $4-6$ months, and then started slowly fading over the next2 years, with at least three superimposed $\sim$1 mag sudden rebrighteningevents. Whereas the amplitude and duration of the maximum is typical for EXors,optical and near-infrared spectra obtained at the maximum are dominated byfeatures which are typical for FUors. Modelling of the accretion disc at themaximum indicates that the disc bolometric luminosity is 43 L$_{\odot}$ and themass accretion rate is $2.5\times10^{-5}$ M$_{\odot}$ yr$^{-1}$, which aretypical values for FUors even considering the large uncertainty in the distance($1.7_{-0.4}^{+0.8}$ kpc). Further monitoring is necessary to understand thecause of the quick brightness decline, the rebrightening, and the otherpost-outburst light changes, as our multi-colour photometric data suggest thatthey could be caused by a long and discontinuous obscuration event. Wespeculate that the outburst might have induced large-scale inhomogeneous dustcondensations in the line of sight leading to such phenomena, whilst the FUoroutburst continues behind the opaque screen.

Gaia21bty: An EXor lightcurve exhibiting an FUor spectrum