The difference between the focal distances of any point on the hyperbola $\frac{{\mathrm{x}}^2}{{\mathrm{a}}^2}-\frac{{\mathrm{y}}^2}{{\mathrm{b}}^2}=1$ is 6.If ($\sqrt{13}$, k) is an end point of a latus rectum of this hyperbola, then k=