  We discuss radiative transitions of a charged kaon to a pion and two photons.
In particular, we have a closer look at radiative corrections for the
$K^+\to\pi^+\ell^+\ell^-$ decays and present the branching ratio of the
$K^+\to\pi^+e^+e^-e^+e^-$ process calculated for the first time at leading
order in the Standard Model.
