A recent lattice prediction of $\varepsilon'/\varepsilon$, with a 2.1 $\sigma$ deviation from the experimental value, has triggered several studies of possible contributions from physics beyond the Standard Model. We have recently updated the SM prediction, including all known short-distance and long-distance contributions, our result $\mbox{Re}\left(\varepsilon'/\varepsilon\right) = (15 \pm 7)\cdot 10^{-4}$ is in complete agreement with the experimental measurement. In addition, we emphasize on the importance of the long-distance re-scattering of the final pions in $K \to \pi \pi$ for a correct prediction of $\varepsilon'/\varepsilon$.