The diminutive winger, 20, made five appearances for the first team during his four years at Stamford Bridge and leaves the English champions after spending last season on loan at Dutch champions FC Twente.
Unwanted Stoch: Former Chelsea winger (left) on international duty with Slovakia
Stoch impressed during his year playing under former England boss Steve McClaren but the Turkish side swooped to snap up the highly-rated youngster just ahead of World Cup kick off.
Fenerbahce are looking to build this summer after coming second in the Turkish Super League, missing out on the final day to winners Bursaspor.
A 1-1 draw with Trabzonspor handed their rivals the title and sparked rioting as fans set fire to sections of the Sukru Saracoglu Stadium in Istanbul.
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