Evaluation of irreducible polynomial in severable variables remains irreducible?

Question

Let $F \in \mathbb{C}[X_1, \dots, X_n]$ be a polynomial in $n$ variables with complex coefficients and $f = F(X_1, \dots, X_{n-1},1) \in \mathbb{C}[X_1, \dots, X_{n-1}].$ If we suppose that $F$ is irreducible, is it true that $f$ is also irreducible ?