I had thought that Pavlos would keep using his current courtesy title as the pretender to the throne?
Per past precedent, the oldest son of a former king becomes the pretender to the defunct throne.
Currently, in Europe there is only one parallel case, that of Serbia, where the son of former king Peter, Prince Alexander, is styled officially, that is, by the very government of Serbia, as HRH Crown Prince Alexander. However, in his case, there are important and significant differences:
1) The Serbian government has formally recognized the Karadjordjevic Family as a nation-building dynasty. This is the reason, in fact, that the crown adorns the Serbian Flag, the Palaces have been returned to the RF and, albeit without constitutional status, the Crown Prince partakes in many state functions, within Serbia and abroad.
2) Although a majority of Serbians are republicans, the history they are taught at school is intricately related to the Karadjordjevic Family for centuries and Karadjordje is linked to the struggle for independence (from the Ottoman Empire) of the Serbian people.
3) King Peter was dethroned illegally.
In summary, the national identity of the Serbian people is tied to the Karadjordjevic dynasty and the Serbian people themselves chose to style Prince Alexander as HRH Crown Prince Alexander.
In the case of Greece, matters are profoundly different. While former king Constantine retains the royal prerrogative to style his oldest son Crown Prince, this is not in agreement with the sentiment of the Greek people and the Greek Constitution makes no provision for titles of nobility - but this doesn't matter as long as the members of the former royal family choose not to be Greek nationals. In view of Greece's membership to the EU, it is most certain that no European Court will ever recognize him as titular king upon his father's death. In a historical sense, however, he will continue to be known as
Crown Prince in view of the fact that at the time of his birth he was a constitutional Crown Prince. This, nonetheless, does not and cannot apply to his morganatic wife, Mrs. Miller, unless former king Constantine elevates her by letters patent to the status of princess [which he would never do because he would lose even the 10-12% of his remaining popularity among the Greeks who, in certain ways, are incurable snobs]. Finally, all these matters are of no interest or concern to the Greek people.