The Knight of the Red Beard (The Cycle of Oak, Yew, Ash, and Rowan)

is book #5 of The Cycle of Oak, Yew, Ash, and Rowan. Is if the final book in the saga.
==Book Description==
Having rebuilt the NordornLand from rubble, Ashen and Gaurin rule justly and fairly over a reinvigorated land. Beloved by their kingdom, they now turn their attention to the next generation of Nordorn royalty.
Responsible Bjaudin, heir to the throne, focuses on his studies and Hegrin, Queen of Rendel, rears her own growing brood. But the youngest siblings, Elin and Mikkel, seem destined to alter the future of the NordornLand—for better or for worse.
Thirteen-year-old Elin craves power, and believes her new alliance with the evil Ysa may help her achieve it.
Eleven-year-old Mikkel stows away on a Sea-Rover ship, hoping for a brief adventure. But when the ship is attacked, Mikkel is taken prisoner, and soon his bonds to the NordornLand are the last thing on his mind.
Through births and deaths, celebration and wars, Ashen and Gaurin have worked tirelessly to bring peace and prosperity to their kingdom. But it appears that this era of peace may be at its end. This final installment of the Cycle of Oak, Yew, Ash, and Rowan brings the series to a thrilling climax worthy of these fascinating characters.
(Description from SashaMiller.com)