Timothée Chalamet can neither confirm nor deny the rumors about his alter ego ... keeping mum when asked whether he's the masked rapper EsDeeKid .

The actor appeared on the "Heart" radio show in the United Kingdom Thursday ... when the hosts asked him straight-up if the rumors about his side career in rap are true. Getty / Instagram @esdeekid

Check out the clip ... Chalamet tightens up -- telling the pair he's got nothing to say about that question before offering the short response, "All will be revealed in due time."

The hosts laugh and try to dive in again by asking about Chalamet's past rap experiences ... but, Chalamet just laughs alongside them -- and doesn't offer up any new info. Instagram / @esdeekid

It certainly isn't a "no" ... but, it sounds like we're not going t

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