You might not think it but even the gorgeous Kate Middleton is a major sufferer of frizzy hair. Yes, really...

She's so open about it that she has even said when she travels across the world on her royal tours, she is more than happy to do her own make-up and outfit styling; her only wish is to have a hairdresser on stand-by to help her manage her locks. 

Sure, her hair may be enviably thick but more often than not, it's the girls with dense locks that tend to have an issue with frizzy fly-aways. However there is a solution, as InStyle's Beauty Director Cassie Steer proves.

As part of our mammoth InStyle Best Beauty Buys 2015 supplement (which is currently on the shelves for free with our March issue), Cassie and her team of experts tried and tested more hair products than you could shake a hairdryer at. And, as part of their winners list, they've found the wonder-product that will help you go from frizzy to sleek in a flash.

In the video above, Cassie shows us just how to use Aveda's Smooth Infusion Naturally Straight serum (£21.50, which will smooth out even the most unruly tresses with ease. 

Starting off with wet hair, squeeze a dollop of the serum onto your hand and run through the mids to ends of your hair, then simply blow dry with a round brush. Yes, it really is that easy! Who needs a session stylist, eh Duchess Kate? 

To finish, use a teeny bit of the serum to give your locks a glossy sheen and voila — you'll never have to worry about unsightly frizz again.

Leaving the house in the morning just got 100% easier. Thank you, Aveda... 

Check out the rest of our amazing beauty how-to videos and all the winners of InStyle's Best Beauty Buys 2015 right here.