A painting by Vincent van Gogh that has been kept in a private collection for 120 years is expected to fetch more than €1 million when it goes up for sale.

Head of a Woman is one of dozens of individual portraits of peasants that Van Gogh painted in the Brabant village of Nuenen while his parents lived there between 1884 and 1885.

The subject, Gordina ‘Sien’ de Groot, also appears in one of Van Gogh’s best known works, The Potato Eaters, which dates from 1885.

It was one of a bundle of 40 paintings that Van Gogh left behind in a crate when he left Nuenen for Antwerp in 1885. The crate was reputedly sold by a local carpenter for one guilder to a scrap dealer, who sold the contents on to the art trader Christian Oldenzeel.

Oldenzeel sold the portrait of De Groot in 1903 to Daniel Pierson, a banker from The Hague, whose family have owned it ever since.

De Groot, who was 30 when she sat for the painting, is the only one of Van Gogh’s subjects whom he mentioned by name in his letters to his brother Theo.

She modelled for Van Gogh 20 times altogether, fuelling local rumours that the two were having an affair. Those rumours intensified when the unmarried De Groot gave birth to a son in October 1885.

Van Gogh vehemently denied having any improper dealings with De Groot, but referred to the incident a month earlier when he wrote to Theo that he had had ‘a great deal of trouble with the reverend gentlemen of the priesthood’.

The Christie’s catalogue for the sale notes the artist’s denials, but remarks that ‘the present work nevertheless suggests a particular tenderness between artist and sitter, evident in the potency of her stare’.

The London auction house expects the painting to fetch between £1m and £2m (€1.1m-€2.2m).