Funny excerpt from a paper I wrote for the great art historian Jonathan Brown. (I got an A.)
Dumbed-down (TLDR) version: 
Apollo (in a tattletale’s smug lilt): Yo Vulcan, Venus is cheating on you with Mars.
Vulcan: Huh?
Venus: Oh, Mars.
Mars: Oh Venus, that’s my p***s!
Vulcan: Gotcha!
Mars and Venus (in unison): Doh.
Source Paintings:
“Velázquez’s Mars Resting has provoked new thought about this adulterous god. Is Velázquez eating his brazen words about painting only course people and avoiding the more “important” subjects? Indeed he is not. He has taken history painting on in his own way.
Only by understanding and assimilating the “Grand Manner” is Velázquez free to reinterpret these stories and bring them closer to the human heart. We can picture this post-coital Mars sitting on the edge of the bed he shared with Venus (perhaps the very same bed of Venus at her Toilet (The Rokeby Venus) and see his expression as ultimately dissatisfied. Though Ovid states that upon catching the adulterous lovers, “one of the gods, undismayed, prayed that he might be shamed like that,” Velázquez’s Mars seems nonplussed by the Pyrrhic victory of his spoilt love affair––perhaps not by the shame of his exposure to ridicule, but by the hollowness of lust fulfilled without greater substance. These two works combined, (though never meant to be a pair), form a thought-provoking denouement to the exhilarating story started by Apollo in the Forge of Vulcan.”
Museum Nerd (>140) 