A recent example of Italian luxury brand Missoni's partnership with the US retailer Target, and the resulting crash of Target's site (due to very high customer demand for Missoni items) made me think of a similar example in Europe.
H&M, a Swedish fast fashion retailer, regularly partners with well-known luxury wear designers, causing major havoc in its stores. It's widely known that most of these collections are bought out in bulk, only to appear later on on ebay -- at much higher prices than originally sold for at H&M.
The Missoni/Target example is an example of Missoni's high brand equity. See some links to the articles about this partnership: