Game of Thrones actors really know how to tweak their fans. Peter Dinklage, aka Tyrion Lannister, may have used his speech for winning the Emmy for Outstanding Supporting Actor in a Drama to do just that.
That's the hint. A longtime fan theory that attempts to resolve one of the many mysteries buried in the show's various plot threads is that Dinklage's Tyrion is a Targaryen.
If he is, then his character will satisfy the Three Headed Dragon prophecy as one of three Targaryens jockeying dragons on the battlefield. If Tyrion is indeed that Targaryen, Jaime Lannister would be his half-brother.
Unlike the show itself, it's really that simple. However, as mentioned above, GoT actors do seem to share a mischievous streak, dangling tantalizing threads of innuendo and rumor in various interviews without ever really springing a leak.
As usual, we won't really know till 2019, and the fans will keep hanging onto every thread for dear life until then.