  Let $G$ be a graph with the vertex set $ \lbrace v_1,\ldots,v_n \rbrace$. The
Seidel matrix of $G$ is an $n\times n$ matrix whose diagonal entries are zero,
$ij$-th entry is $-1$ if $ v_{i} $ and $ v_{j} $ are adjacent and otherwise is
$ 1 $. The Seidel energy of $G$ is defined to be the sum of absolute values of
all eigenvalues of the Seidel matrix of $G$. Haemers conjectured that the
Seidel energy of any graph of order $n$ is at least $2n-2$ and, up to Seidel
equivalence, the equality holds for $ K_{n} $. We establish the validity of
Haemers' Conjecture in general.
