While the Filmation series for He-Man was known for their re-use of animation-cycles and model-sheets for multiple characters, the Mike Young Productions version of the cartoon did not shy away from re-using character-models.
In season 1 episode "The Island", Man-At-Arms is injured while visiting his mentor Dekker alongside Teela and Prince Adam. Man-At-Arms asks Teela to remember her lessons and we cut to a flashback of a Younger Teela sitting in a class-room that was being taught by Duncan.
Behind Teela, we see a black-haired boy who doesn't look all that excited to be in the class.
While looking at the episodes recently, I noticed that in the moral-segment for season 2 episode "Of Machines and Men", the same black-haired boy appears again.
In the scene the boy is saved by Ram Man and doesn't have any dialogue just like in the flashback with Teela. This re-use of a background-character is of course no big deal when comparing the reused material Filmation did, but personally I thought it was interesting to discover that this kid either had time-traveling abilities or simply hasn't aged at all.