(CNN)With plot lines that would make even the writers of Game of Thrones scratch their heads, the 2021 European summer transfer window may very well have been the best one ever.

Not only did the unthinkable of Lionel Messi leaving Barcelona happen -- moving to pastures new at Paris Saint-Germain -- but his long-time rival Cristiano Ronaldo also secured a remarkable transfer, returning to Manchester United in an incredible U-turn after it had been widely reported he would be joining bitter rival Manchester City.