Crown Prince Wilhelm, though not strictly a pretender until his father Wilhelm II died, was interested in trying his hand at this stunt in 1932 Germany before his father forbade it. Have Hitler trip down the stairs before anyone has ever heard of him and the monarchist German National People's Party is likely to be the leading party of the German far right. If, following the Wall Street Crash, the Nationalists do pretty well in elections to the Reichstag (not necessarily as well as the OTL National Socialists did, but well enough to become a very major party, due to the radicalising effect of extreme economic tumult and due to lacking any effective competitors on the far right) and they pick a leader like Lettow-Vorbeck or Treviranus who's more 'in' with the 'respectable' German nobility and monarchy than Hugenberg—a PoD that only requires killing off two people, Hitler and Hugenberg, at the appropriate times—they may well be able to persuade him to defy his father and compete anyway, as they're powerful enough that it seems worth a try. He already often didn't do what his father wanted him to do, it's actually quite surprising that he was obedient on that point in OTL. Under those circumstances, since Hindenburg was a hard-line monarchist, he could very probably have been persuaded to not run again and endorse the Kronprinz for the Reich Presidency.
If the Nationalists did well enough in the Reichstag that, as with the National Socialists in OTL, there arose an 'anti-republican majority' (far left + far right) that made the pro-republican parties incapable of blocking Hindenburg's increasing tendency to rule by presidential power, there's easy cooperation between them and Hindenburg, there's a somewhat OTL-esque rise of the far right to power (but with much easier collaboration with the cabal around Hindenburg and the Nationalists than in OTL where the National Socialists were involved too) and it's easy for the monarchy to be restored. If the Nationalists didn't do well enough for there to be an anti-republican majority, the pro-republican parties would be stuck governing the country and making themselves even more unpopular, ably aided by their own likely difficulties in coming to a consensus (given the non-negligible differences of ideas, to put it mildly, between democratic socialists and some rather hard-right conservatives of parties including the one of which Brüning in OTL was a member) without a figure from above forcing the way; so it's reasonably possible for the Kronprinz to be elected even if the coalition candidate isn't eliminated before the KPD candidate, let alone if he is. In that case, with Nationalist street thugs roaming all over the place beating up people they don't like, it's only a matter of time before there's a confrontation between the Presidency and the Chancellery, sparking a conflict which the Nationalists—with a much greater support base in the Army, plus the Stahlhelm and any other right-wing street organisations they've picked up—are extremely likely to win.
Result: Destruction of German democracy and restoration of the Hohenzollern monarchy in Germany, under a nice pleasant (sarcasm alert!) anti-Semitic ultranationalist reactionary regime. Yay! Yay…?
As for international results, I think it would be a significant blow to fascists and a major aid to reactionaries across the world as the leading force of the far right; it would be a sea-change from dictatorships like Mussolini's to dictatorships like Franco's and Pinochet's. Plenty of right-wing people who in OTL criticised the National Socialists and the Italian fascists might well not criticise the Nationalists. The international reaction would be pretty similar to the international reaction to Hitler's rise to power in OTL: the left and some elements of the non-extreme right would be appalled, the far right would be cheering, and other elements of the non-extreme right—including people like Churchill—would withhold judgement and later decide whether to cheer them on for stopping socialism or to despise them for being expansionist/breaking their word/some reason or another.
(I've long argued, for a variety of reasons, that a Nationalist takeover, rather than a communist Germany or the highly optimistic 'Weimar survives' idea, is the likely result of killing off Hitler early, though I don't think this particular way is the only or even the most probable way for it to occur.)
