The Diet of Augsburg rules that the Protestant princes of Germany
must conform, by disowning their heretical attachment to Martin
Luther and his doctrines, by 15th April 1531.
Citation:
Editors. "Protestant princes ordered to conform by 15th April 1531".
The Literary Encyclopedia. First published 01 November 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=14451, accessed 23 May 2013.]