RMO proving problem

Two circles $Ω_{1}$ and $Ω_{2}$ with centers $Ο_{1}$ and $Ο_{2}$ respectively, intersect each other at points $C$ and $D$ . Two tangents $λ_{1}$ and $λ_{2}$ are drawn at point $C$ , perpendicular to each other, cutting $Ω_{1}$ at point $A$ and $Ω_{2}$ at point $B$ respectively. Points $Ο_{1}$ and $Ο_{2}$ are joined, thus intersecting $Ω_{1}$ and $Ω_{2}$ at points $X$ and $Y$ respectively. Now lines $AX$ and $BY$ are drawn which intersect each other at point $G$ .

Find the measure of $∠GCA$ and prove it.