13 Primes || TFO

Sentinel is ambitious, but not stupid. He understands that as long as Zeta Prime lives and is beloved by the people, he has no chance of achieving absolute power. His plan with the Quintessons and the "Maw of Unicron" cave is the final chord, but for now he plays the role of the perfect student.

Hypocrisy: The dance scene is part of his strategy. He makes Zeta feel like a great mentor to lull him into a false sense of security.
Relationship to Thirteen: Sentinel despises Thirteen. To him, Thirteen is a "backup option" whom Zeta once tried to turn into a hero. Sentinel sees Thirteen as a threat only if he suddenly decides to reveal the truth. Therefore, Sentinel treats Thirteen with exaggerated politeness, but with a condescending air, like an older brother condescendingly patting his younger brother on the helmet.

Thirteen is not a villain. His conflict is a tragedy of loyalty that has gone unnoticed.

Feelings of Uselessness: He remembers the times when Zeta discussed strategy with him while they patrolled the Energon mines together. Now, Zeta doesn't even ask his opinion at Prime Councils.
Jealousy and resentment: Thirteen isn't jealous of power, he's jealous of attention. He sees Sentinel literally absorbing Zeta's every word, and this fills Thirteen with a mixture of bitterness and anxiety. He's the only one who notices the flicker of cold satisfaction, not gratitude, in Sentinel's eyes when Zeta praises him.
Inner Voice: Thirteen tries to warn Zeta, but phrases it hesitantly, afraid of appearing envious. His words end up sounding like a grumble, and Zeta waves him off: "Don't be so gloomy, brother. Sentinel's just trying."

Zeta Prime isn't a villain, he's simply blinded by his desire to see the best in his student.

Leader's Blindness: He sincerely believes he's making Sentinel a better person. He doesn't notice that Sentinel is copying his gestures and manner of speech to become his mirror image.
Guilt towards his brother: Somewhere deep down, Zeta feels guilty towards Thirteen. That's why he stages such public moments, like the dance in the picture, to show everyone, "I love my brother, I haven't forgotten him." But he does it so clumsily and rarely that it only hurts Thirteen more.