South Dakota Codified Laws
Chapter 02 - Suretyship
Section 56-2-2 - Apparent principal may show that he is a surety.

56-2-2. Apparent principal may show that he is a surety.
One who appears to be a principal whether by terms of a written instrument or otherwise may show that he is in fact a surety except as against persons who have acted on the faith of his apparent character of principal.

Source: SDC 1939, ยง26.0203.