The Sherbrooke Twins by Catherine Anderson (Sherbrooke Brides #7)

James, twenty-eight minutes older than his brother, is the heir--a student of astronomy who rides like a centaur, and unlike his brother, Jason, enjoys learning the ropes of managing his father's estate. He no longer sows excessive wild oats, as his neighbor, Corrie Tybourne-Barret, a brat he's known since she was three years old, looks forward to doing since she turned eighteen...As for Jason, he swims like a fish, loves horses, wants to start a stud farm, and sows more oats than a man should be allowed--until he finally meets a girl who stops him in his tracks. Adventures compound in this "madly romantic, supremely sexy adventure" (Booklist), with rich, colorful characters and a confounding mystery. Paperback, 2004 Goodreads: 3.93