I would like to write the following for the legend of a curve :

$$ \theta_n = \frac{\pi}{2}$$

However, when I write this in mathematica :

Style["\[Theta]n=" <> ToString[Pi/2]]

The fraction goes under the $\theta_n$ like on this picture :

How can I do to make mathematica write properly what I want ? I am looking for a very simple solution.