The following is inspired by the OTL reputed Anti-Nazi stance of Wilhelm II's other sons specifically Eitel Friedrich, Oskar and Adalbert.
In the unlikely scenario of Germany becoming a constitutional monarchy after WW1 (let alone post-WW2), the challenge is to get either one of Wilhelm II's other sons mentioned above to succeed him as figurehead King.
Bonus points if one of the above (or even a surviving Joachim) dies in suspicious circumstances likely by the Nazis who proceed to pick either Crown Prince Wilhelm (his predecessor's reign being cast as illegitimate and his ascension to the throne viewed as a historical corrective) or August Wilhelm as a successor more supportive of Nazism. Thereby leading the other surviving Anti-Nazi Princes to flee the country until the aftermath of WW2, where one of them takes over as King and acts as a stabilizing force during the post-war era onwards.
In the unlikely scenario of Germany becoming a constitutional monarchy after WW1 (let alone post-WW2), the challenge is to get either one of Wilhelm II's other sons mentioned above to succeed him as figurehead King.
Bonus points if one of the above (or even a surviving Joachim) dies in suspicious circumstances likely by the Nazis who proceed to pick either Crown Prince Wilhelm (his predecessor's reign being cast as illegitimate and his ascension to the throne viewed as a historical corrective) or August Wilhelm as a successor more supportive of Nazism. Thereby leading the other surviving Anti-Nazi Princes to flee the country until the aftermath of WW2, where one of them takes over as King and acts as a stabilizing force during the post-war era onwards.