Continuity mistake: After they tear her dress before the ball, Stepmother gets into Cinderella's face and points her right finger at her, but in the next shot it's her left finger pointing up at Cinderella's face.
Continuity mistake: When the fairy godmother changes Cinderella's shoes, there is a shot where you see Cinderella's bare legs and feet in the glass slippers and she then gets into the carriage. However, in a later scene where the Prince slips her glass slipper back on in the palace gardens, a shot shows her wearing tights, which the fairy godmother failed to provide her with.
Answer: Even if he did, he didn't know she was the stepmother of Cinderella.