I'm confused about verb tenses in a complex sentence. Why is present perfect tense used in this? Here is the sentence below. It is written in a workbook for TOEIC. We regret to announce that Mr.Charles has resigned his position as senior sales manager, effective next Monday. I don't know why the present perfect tense, "has resigned" , is used in the dependent clause. The time Mr.Charles is going to leave his position is future, next Monday, so I cannot understand it. Does anyone explain how to use verb tenses in this case? If it is the present tense "resigns", future tense "will resign", or future perfect tense "will have resigned", these tenses are not correct in grammar?