The English model wears a figure-hugging red dress in the teasing clip, which promises viewers that they could "have a pair like Kelly's", before she reveals a pair of the official charity socks.
Joking that the socks are the secret behind her famous assets, Brook says: "I can't believe that the secret's finally out there, but now that it is, everyone should know that the Sport Relief Socks are an essential item in my styling kit. I take them everywhere with me, to the gym, when I'm going shopping or on a night out with the girls."
Watch Brook's 'Perfect Pair' advert below:
The Sport Relief socks are available to buy from Sainsburys for £2.50, with half the cost going to the charity.
Featuring musical performances and comedy sketches, the Sport Relief telethon takes place tonight on BBC One from 7pm.
> Christine Bleakley, Frank Lampard meet Outnumbered for Sport Relief
> England footballers take Omelette Challenge for Sport Relief: Pictures
