What could be the verdict

Mr. A purchased a land and made a registered gpa and mentioned as irrevocable gpa and before gpa a sale agreement was also done to Mr B. Mr. B sold that land to Mr.C after long years of gap. Mr. C was about to register the land by on him by that time Mr. A cancelled gpa on Mr. B and now the issue is in court what could be the verdict of court on this matter asking this opinion coz my friends has this case in court he told not to mention any names but just facts and seek some previous judgements on this type of matters so I have posted if it hurts pls forgive and answer