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We report the discovery of two Einstein Crosses (ECs) in the footprint of theKilo-Degree Survey (KiDS): KIDS J232940-340922 and KIDS J122456+005048. Usingintegral field spectroscopy from MUSE@VLT, we confirm their gravitational-lensnature. In both cases, the four spectra of the source clearly show a prominenceof absorption features, hence revealing an evolved stellar population withlittle star formation. The lensing model of the two systems, assuming asingular isothermal ellipsoid (SIE) with external shear, shows that: 1) the twocrosses, located at redshift $z=0.38$ and 0.24, have Einstein radius $R_{\rmE}=5.2$ kpc and 5.4 kpc, respectively; 2) their projected dark matter fractionsinside the half effective radius are 0.60 and 0.56 (Chabrier IMF); 3) thesources are ultra-compact galaxies, $R_{\rm e}\sim0.9$ kpc (at redshift $z_{\rms}=1.59$) and $R_{\rm e}\sim0.5$ kpc ($z_{\rm s}=1.10$), respectively. Theseresults are unaffected by the underlying mass density assumption. Due to size,blue color and absorption-dominated spectra, corroborated by low specificstar-formation rates derived from optical-NIR spectral energy distributionfitting, we argue that the two lensed sources in these ECs are blue nuggetsmigrating toward their quenching phase.

Discovery of two Einstein crosses from massive post--blue nugget galaxies at z>1 in KiDS