The starting point for great hair is not the cut, or the styling products, or the lack of humidity (although that helps). It's more basic.
Kate doesn't have split ends. For princess-worthy tresses, trim often (and not yourself). Visit a stylist every four to six weeks for a little touch up.
There are plenty of salons where you can get a simple trim for a reasonable price.
It will make your hair look smooth (no dry, no stringy, no split ends) and bouncy, because it's not being pulled down by dead, frizzy weight.
And while you're there …