Agatha Christie's family jewels are set to go under the hammer in October (14).

A 19th century diamond brooch and an engagement ring thought to have belonged to the English crime writer's mother are expected to fetch up to $13,600 (£8,000) and $8,500 (£5,000) respectively when they go up for sale at Bonhams auction house in London.

The owner found the family heirlooms in a locked trunk she bought from a yard sale at Christie's former home in 2006. She paid $170 (£100) for the box, which came without a key, and only discovered the jewels in 2010.

The auction will take place on 8 August (14).

Christie, the creator of detective character Hercule Poirot, died in 1976.