El Gordo (ACT-CL J0102-4915) is an extremely massive galaxy cluster ($2.13^{+0.25}_{-0.23} \times 10^{15} M_{\odot}$) at redshift z=0.87, composed of two interacting subclusters with mass ratio 1.52. Hydrodynamical simulations of the interaction suggest that $V_{\textrm{infall}} \approx 3000$ km/s is required to match the observed luminosity and morphology of El Gordo. In this work, we determine the probability of finding a similar object $-$ in terms of total mass, mass ratio, redshift, and infall velocity $-$ in a $\Lambda$CDM context using the cosmological simulation "Jubilee". We find that the probability of detecting at least one candidate in the simulation box is of $7.33 \times 10^{-8}$ (i.e, El Gordo is in 5.38$\sigma$ tension with the model). The probability decreases to $1.06 \times 10^{-8}$ (5.72$\sigma$ tension) when also taking into account the Bullet Cluster. These systems arise naturally in a Milgromian dynamics (MOND) cosmology with light sterile neutrinos.