Blooms of Darkness by Anna Applegate

Magic is power, and power is status. With no exceptions, save one: Princess Illiana Dresden, the sole heir of Brookmere.

Despite being born void of magic, Princess Lana remains in the public eye, earning the love of her people. Keeping her secret is essential for maintaining her position as heir, so she wears a mask of the perfect princess, even when faced with the impending marriage trials, despite her protests.
Guided by a prophecy given to Lana at birth, the king enacts the trials to secure the succession of the throne. The centuries-old tradition brings Fae from across the land, and not all of them have the princess’s best interest in mind. Most couldn’t care less about winning Lana’s heart as long as they become King in the end. If they make it that far. Risk of death or not, once begun, there is no stopping the marriage trials. Even if continuing becomes dangerous to the princess herself.
From the moment they meet, one contender in particular crawls under Lana’s skin, and not just because he dared to hold her at knifepoint. Kade Blackthorn possesses his own secrets, along with an obnoxious arrogance and a frightening amount of power. The shadow-wielding stranger knows too many of Lana’s secrets, and it’s only a matter of time before he uses her to get what he really wants—the crown.
But with darkness spreading wildly across the lands, she may not have a choice but to trust him. Along with the few she calls friends, they might prove to be the only ones who can save Brookmere.
If it can be saved at all.