1926 - Canada Has Three Prime Ministers In Less Than Four Months

Due to the Constitutional Cris of 1926 (also known as the King-Byng Affair) (see here), the Prime Minister of Canada William Lyon Mackenzie King resigned on June 28. 

William Lyon Mackenzie King, Prime Minister of Canada until June 28, 1926.

The leader of the Conservatives, Arthur Meighen, becomes Prime Minister for the second time.

Arthur Meighen, Prime Minister of Canada between June 29 and September 25, 1926.

Source of image: https://en.wikipedia.org/wiki/Arthur_Meighen#/media/File:Former_PM_Arthur_Meighen.jpg

Source of image: http://torontoist.com/wp-content/uploads/2015/09/20150926starfrontpagejuly29.jpg

As Prime Minister, Arthur Meighen is unable to achieve confidence in the House of Commons and a federal election is called for September 14.

Source of image: http://torontoist.com/2015/09/historicist-king-vs-meighen-for-the-fate-of-canada/

William Lyon Mackenzie King runs under the coalition of Liberals-Conservatives and wins the federal election on September 14 becoming Prime Minister on September 25.

From an editorial cartoon from September 1926.

Source of image: http://torontoist.com/wp-content/uploads/2015/09/20150926cartoonstarrunning.jpg