"Oh, Joey, that smells divine." Iridescence breathed in deep, basking in the scent of perfectly brewed coffee. "But, of course, friends share, right?"

"Don't you even dare-" Cuppa Joe started, but Irie had already dipped her tongue in his coffee.

"…Y'know, I guess it's reassuring that even princesses are capable of dick moves." Joe sighed, but Irie knew it was mostly show. "That's not gonna stop me from drinking the rest though." Boldly, he drained the rest of the mug just to spite her.

"You're so gross, Joey."

"You're worse, bug-butt." Joe stuck his tongue out at the princess, and Irie giggled. "You might have acid glands, but you don't have cooties. I know that from experience." He sent her a sly wink.

"Joey!" Irie held a hoof up to her muzzle, feigning scandal and hiding a grin. "…Careful, little pony. You're speaking to a princess."

"I'll hold my tongue when you learn to watch yours, princess." Joe rolled his eyes and turned to pour himself another brimming cup. Quickly, he snatched it out of reach before Irie could steal a sip again, and quickly trotted away. Shamelessly, Iridescence eyed his flank as he left, and rose to follow.

"No promises, Joey."

~
you know at first i had Cuppa Joe (NextGen son of Donut Joe) as just kind of a one-off character but I decided to give him a bigger role in the pandoraverse

He lives in Canterlot, and he's very best friends with Princess Iridescence. They befriended each other as awkward pre-teens (Joe was pudgy and short, Irie was tall and gangly as hell), brought together by mutual snarkiness and love of immature sex jokes, and they've been inseparable since

They're total kindred spirits-both are huge flirts, playful, living in the moment, confident, vain, snarky, and too smart for their own good. Also both can hide their emotions like champs…except from one another. They bond over coffee, sweet snacks, cheesy old movies, a love of cats, a love of messing with ponies, and mutual frustration with the snobby aristocrats of Canterlot. In wintertime, Irie uses Joe as a personal snuggle furnace to combat the dreaded cold. They're definitely friends with benefits (in a very open relationship) and it's juuuust about the worst kept secret in Equestria. They also act as each other's wingponies when it comes to picking up dates, and are each other's personal confidantes

I'm paraphrasing ideas suggested by the evil creative overlord roboheather

Princess Iridescence is the daughter of Princess Celestia and Queen Chrysalis
Cuppa Joe is the son of Donut Joe and Cinnamon Chai (a mare appearing in the episode Rarity Investigates)