Angles of Orthic Triangle of Acute Triangle

Theorem
Let $\triangle ABC$ be an acute triangle with sides $a$, $b$ and $c$ opposite vertices $A$, $B$ and $C$ respectively.

Let $\triangle DEF$ be the orthic triangle of $\triangle ABC$.

Then the angles of $\triangle DEF$ are $180 \degrees - 2 A$, $180 \degrees - 2 B$ and $180 \degrees - 2 C$.