No, not that truth, though she is quite correct.
One day, Princess Celestia ate 37 Rice Krispie Treat packets. Unsurprisingly, the next day, she farted a lot, because those make you fart. The whole Palace smelled like Celestia farts. And her farts were extremely rank. Most ponies were too polite and scared of her to complain, but as we all know from that one episode where she switched Celestia and Luna's cutie marks, Starlight Glimmer doesn't particularly respect or fear Royalty.
So she spoke the truth.
No, not that truth, though she is quite correct.
The other truth. "Celestia, if you're going to fart this much, you should really either teleport outside to do it, or at least go buy some Febreeze or Poo-Pourri or something. Your farts are worse than those of a manticore with food poisoning.
It was true. Her farts did stink pretty bad. I was supposed to have a makeout session with her that afternoon at 4:30, but elected to instead reorganize my stamp collection with Twilight's help. In Ponyville, quite distant from Stinkerlot Castle.
Philately is, after all, one of my many special talents.