Let \( P \) be a parabola with vertex \( (2,3) \) and directrix \( 2x+y=6 \). Let an ellipse \( E:\ \dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1, a>b \), of eccentricity \( \dfrac{1}{\sqrt{2}} \) pass through the focus of the parabola \( P \). Then, the square of the length of the latus rectum of \( E \), is;
