How to make persons or objects appear in a Video project

Hello Adobe-Community,

There's tons of information on the net on how to make unwanted persons and /or objects disappear (as with Kyler Holland here) - my question is how to make a character appear! In a video sequence for instance a character is talking when all of a sudden another character is introduced into the scene by gradually fadeing in.

I tried to solve this with the gradient wipe feature, however it seems to me this only works when the object was there in the first place. Is there any workaroung how to do achieve this effect?

Thanks for any piece of inspiration out there!