In the diagram, ABCD is a square and ABE is an equilateral triangle constructed inside the square. The diagonal AC intersects the side BE at point F. What is the size of angle $\angle BFC$?
Diagram Description: A square ABCD is drawn. Its vertices are A (top-left), B (top-right), C (bottom-right), D (bottom-left). An equilateral triangle ABE is drawn inside the square, so vertex E is below the side AB. The diagonal from A to C is drawn. The line segment from B to E is drawn. These two lines, AC and BE, intersect at a point labelled F.