I, too, must acknowledge that the discussion deviated somewhat and I am also guilty for that.
But I felt that Warren's remark of "unequal" marriages being treated differently, at least by the Greek Royal House was/is
quite a challenging historic fact and a case for analysis. The standards used and adopted by the Greek royal family varied widely and wildly - from utterly strict (Peter's case) to profoundly relaxed (Christopher's case), to suit the circumstances, I guess.
This discussion, however, was/is very pertinent to Prince Peter who was the heir to Prince George and Princess Marie. Prince Peter was no ordinary royal personage. Apart from his imposing elegant appearance, he was a highly educated and sophisticated man with tremendous culture and anti-conformist - like mother like son.
Although he was maintaining the Aixoni Palace [Ανάκτορα Αιξωνής], in the Glyfada area, just north of the old Hellinikon International Airport in Athens, he would come and go without anyone knowing his whereabouts. In the 20 years from Paul's ascent to the throne (April 1947) to the royal family's departure abroad (December 1967), the only public and official appearance of Prince Peter was at the funeral of King Paul - he walked with the cortege standing to the right of Princess Irene (then Diadoch) as next in the Line of Succession. I understand in fact, that even in the solemn swearing-in ceremony of Constantine as king conducted by the Archbishop, at the Athens Palace, Princess Irene and Prince Michael were also in attendance, but not Prince Peter. It is, therefore, crystal-clear that he was banned or, at least, ostracized from and by the Palace.
By the way, Prince Peter was quite popular among the Greek people due to his education and culture and the way he was treated [or perceived to be treated] by the Palace was yet another reason [fair or unfair] that fed into the people's negative attitude toward Queen Frederika.