A little mystery

"-I had a problem last week, said Mr Hind to his friend the inspector.

When my father died, I inherited his fortune of several million pounds.

But, last week, Gregg came to see me.

He used to be the gardener until I fired him in December.

He told me that, just before my father died, he was working outside his window and he heard

Dad drawing up a new will in favour of my brother.

My father and I had argued about something at the end of November,

so it was possible that he decided to alter the will.

Gregg told me that the document was in his possession and that he would sell it to

me for fifty thousand pounds.

He said it was dated November the thirty-first, three days after the first will,

so it was worth a lot of money to me.

When I refused, he tired to bargain with me. First, he asked for twenty-five thousand pounds,

and then, finally, ten thousand.

- I hope you didn't give him anything, said the inspector.

- Only my foot in his backside", said Hind.

What was Gregg's mistake?