Help Identifying Small Part from Trek Domane w/ Ultegra

[dlm2182]

Hi All,
I have a Trek Domane SL 6 (Ultegra groupset). When changing my back tire after a flat, the small part in the pictures below came off of the bicycle. Not sure where it belongs, nor its function. Any help identifying it would be greatly appreciated!
Many thanks!
David

 

[iluvmybike]

It looks almost like a pawls from a freehub - but that would only come out of you removed the freehub - ????