The Prince and the Omega by Penelope Peters

Rowan’s not royalty – and that’s fine by him
.
Omega Rowan Thornton has never been so glad he’s not considered royalty. Especially since his best friend Princess Celia is stuck bonding with a foreign prince she’s never even met. Celia’s solution? Ask Rowan to flirt with someone, anyone, during her engagement ball so she can live a romantic entanglement vicariously through him.
Well, that’s what best friends are for, right?

Gus is royal to the bone – and he’s never regretted it before.
Prince Gaspar – better known as Gus – isn’t the type of alpha to fall in love at the drop of a hat, or at the staged farce of a romantic ball. He’s agreed to an arranged marriage because it’s his duty – not his desire. When his half-brother suggests he take a last chance at having what he really wants before getting tied down to a foreign princess, Gus has no intention of following through… until he meets the handsome omega commoner with the adorable smile.

It’s not like Gus is going to lose his heart or anything, right?
It was only a single night – but the consequences could be greater than their lifetimes.
Gus and Rowan both know that a lifetime spent together is impossible – but for a single hour, they just don’t care. One night of giving into their passion has consequences neither of them anticipated… but will it dismantle the fragile truce between their countries? And will one courtier’s jealousy end up destroying everything they both hold dear?