The nickname of the King of Europe is indeed not mere boasting. They have proven it by entering the final eight times since 1998, and eight times they have won. And until now, if Real Madrid had passed the semifinals and then entered the final, they would be the champions.
They are specialists in Champions League finals, so I don't want to argue with that. Real Madrid rarely fail to win the Champions League when they get to the final, but I think their era of dominance in the Champions League will end soon after Manchester City have broken the curse.
I think Real Madrid will not be as strong as before after they no longer have many golden players like Benzema and several other players. Indeed, they have a lot of quality players, but experienced players like Benzema, Modric, Kroos are the spirit of a good performance for Real Madrid. Madrid will realize that, so I think they will still miss the Champions League final in the next few seasons unless they play very badly against Madrid in the Champions League.
Luckily this season Man City can defeat Real Madrid in the semifinals, otherwise Real Madrid will definitely win the 15th UCL trophy.
Manchester City didn't make it by luck, but they have proven themselves better than Real Madrid by the form of it. Madrid played badly, even worse when they played the second leg of the semi-final at the Etihad Stadium.