A Kannappan-cosine functional equation on semigroups

We determine the complex-valued solutions of the Kannappan cosine functional law $g(xy{z}_0)=g(x)g(y)-f(x)f(y)$, $x,y\in S$, where $S$ is a semigroup and $z_0$ is a fixed element in $S\mathrm{.}$