Answer: His memory behaviour suggests retrograde amnesia
Explanation: K.C is presently suffering from amnesia, most especially the selective retrograde type. This is because he can't remember traumatic events from the past, before the accident.
His brother's death must have being a traumatic experience for him, it would have been a time in his life that he wanted to delete and remember no more.
He must have really loved his brother which is also suggestive of why he is unaware of happenings surrounding his brother's death.