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I think Textsecure[1], the predecessor of Signal, is even older (2010)

And Wikipeida also says that the first version of the Signal Protocol is from 2013[2]

[1] https://en.wikipedia.org/wiki/TextSecure [2] https://en.wikipedia.org/wiki/Signal_Protocol

So Telegram launched by about a month early, but the people behind Signal had released prior art earlier, and merely the protocol a few months later, but the Signal app didn't come out until 2015 according to Wikipedia.

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