The 22 year-old said he hasn't been impressed with her rear as he would like it to be bigger.
He told UK newspaper The Sun: 'I've not actually got what all the fuss is about. I prefer a bigger bum. I'm definitely a bum man but she's not doing it for me. Sorry Pippa.'
Middleton sparked a worldwide storm when she wore a figure-hugging Alexander McQueen gown for her sister Kate's wedding to Prince William in April.
However, the rapper said there's another star who he does like - Cheryl Cole.
He said: 'I fancy her, she's a good looking girl.'