The equations of two circles, $\mathrm{C}_{1}$ and $\mathrm{C}_{2}$ are $x^{2}+y^{2}+7 x-10 y+31=0$ and $x^{2}+y^{2}-x-6 y+3=0$
respectively. Find the equation of the circle, $\mathrm{C}_{3}$, which passes through the intersection of the circles $\mathrm{C}_{1}$ and $\mathrm{C}_{2}$ and has its center on the line $\ell$ with equation $\mathrm{x}-\mathrm{y}-2=0$.