South African Constitution of 1961
The Constitution of 1961 (formally the Republic of South Africa Constitution Act, 1961) was the fundamental law of South Africa for two decades. Under the terms of the constitution South Africa ceased to be a Commonwealth realm and became a republic, albeit, temporarily, outside the Commonwealth of Nations from 1961 to 1994.
Source: Wikipedia — South African Constitution of 1961 (CC BY-SA 4.0)