MLA

Koch, Frederick R. (Frederick Robinson). Caraman-Chimay, Alexandre de, Princesse. Box 48, folder 987. [ca. 1903]-[ca. 1917], n.d.. https://collections.library.yale.edu/catalog/16600548.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 48, folder 987"])([ca. 1903]-[ca. 1917], n.d.)[Caraman-Chimay, Alexandre de, Princesse]. https://collections.library.yale.edu/catalog/16600548.