He-Man and the Masters of the Universe (1983)

S01E43 The Royal Cousin

Prince Adam's cousin, the insufferably arrogant Prince Jeremy, comes to stay at the Royal Palace and soon begins to irritate everyone with his obnoxious attitude and entitled demeanor. When Evil-Lyn and Tri-Clops show up, they cleverly exploit Jeremy's spoiled nature to manipulate him into unwittingly assisting them in their plan to infiltrate Grayskull.