Monty python's Holy grail 2: Lost in time(canceled)

Two scientists enter a room. In front of them is the portal maker. They turned to the left to go up some stairs and they find themselves in an office overlooking the portal maker. In front of the main window was a shadowy figure.
Figure: How are the portals?
Scientist 1: They are working as designed, but they're unpredictable.
Figure: What do you mean by that?
Scientist 2: We've collected some data. Turns out each time we turn this thing on, it brings in a random figure from the Arthurian age.
Figure: Like who?
Scientist 2: The first one we found was prince Herbert of swamp castle. Then we found Tim the enchanter, but he seemed to be spying on our secret conversation.
Figure: Do you know if he told anyone about it?
Scientist 1: He seems to have told King Arthur.
Figure: He's here?
Scientist 1: That's right, and he's accompanied by four of his knights and a peasant. They were arrested earlier today.
Figure: What for?
Scientist 2: Well, according to the news, they were heading to the museum of the round table.
Figure: Knowing that king, he must have been after Excalibur. And possibly the grail model. At least the model should get him off track so I can find the real one.
Scientist 2: Well, about that, we're getting closer and closer to it. But the original portal got it trapped between time itself.
Figure: I know that. That's because the portal was still experimental at the time.
Scientist 2: Also, someone is helping Arthur and his knights.
Figure: Who?
Scientist 1: Someone by the name of Grace Allen.
Figure: Hm. Those knights will get in the way, and that woman is helping them. But I have a plan. I brought someone of his times in an hour ago, and I'm refitting him as we speak.
Scientist 1: Who?
Figure: The black knight.
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The black knight returns! A mystery figure is the one behind the portals. Who is it?