Why is the relationship between Bayern and Real Madrid so good?

These two teams have a long history. From the league match between Bayern Youth Team and Real Madrid Youth Team to today's friendly match, the relationship between Real Madrid and Bayern has always been very friendly. The game between the two teams is also one of the most exciting games in football history. In addition, the fans of the two teams also have a deep friendship. They often communicate with each other and always support each other. Moreover, the two teams have also cooperated in the transfer market in recent years, so it can be said that the relationship between Real Madrid and Bayern is still relatively harmonious.