From "Over Sea, Under Stone"
These three siblings have just been through this big adventure with their great uncle (not actually related, he's a family friend) and they've found this grail that's part of a big battle between good and evil
And they're at this museum opening where the grail is on display and the youngest sibling looks across the room at their great uncle and suddenly realizes that his name is similar to Merlin and at that moment the great uncle looks back at him and gives him a knowing look
And the two older siblings are wondering if they'll ever know what the grail and everything all means, and the youngest sibling says "I think we shall know...one day"