The Knight was seen protecting the Golden Apple. He was the major foe when the squires competed to protect the princess. Little did any of them know that the Mysterious Knight was really King Gregor in disguise.
As it turns out, his most formidable opponent during this competition turned out to be Princess Calla herself, who entered in disguise to avoid being shackled with a protector. Once Gregor learned the whole situation, he was deeply impressed at how formidable his daughter had become.