I recommend that you read his lecture on "black holes an baby universes" - it deals with exactly this topic in much more (still understandable) detail. To put it very simply, he believes that matter sucked into a black hole will create a new "baby" universe inside it, which then must somehow re-emerge into our universe when the black hole evaporates.
There is also many more interesting theories, such as how black hole radiation, which caused by the uncertainty principle, must increase massively as the black hole gets smaller. As the position of particles inside the black hole becomes better and better defined (since the black hole is smaller), their velocities become more and more unknown - such that a greater number will travel faster than the speed of light and escape beyond the event horizon.
And then he goes on to talk about what happens when a black hole dies (i.e. huge explosion), how they could form wormholes/be used for time travel, how they fit in with his theory of imaginary time, ... lots of strange stuff.
I just finished reading it recently, as I want to get as many maths/science books read as possible before my interview for Cambridge University in a couple of months... if you know of any good, relevant books that I could read, please let me know