An archive of love letters written by the celebrated British artist Lucian Freud has sold with outstanding results at Sotheby's.

Freud's letters are dotted with illustrations and insights into the artist's mind

The letters formed part of the Contemporary Art Day Sale on February 13 in London, following on from the evening auction that saw Freud's Head on a Green Sofa sell for £2.9m ($4.9m).

The letter archive provided a fantastic opportunity to own items from the artist at a modest price. Estimated at £3,000-5,000, the increasing demand for Freud's work pushed bids to £122,500 ($204,653) - a 2,350% increase.

Freud's sketch of Felicity Hellaby, his one-time girlfriend and fellow art student

Freud wrote the letters in the early 1940s to his girlfriend and fellow art student, Felicity Hellaby, who is also the subject of some of his earliest known paintings. Dotted with illustrations and charming insights into Freud's personality, they are a superb artefact from Freud's early career.

Also selling were three drawings that Freud gave to Hellaby, which achieved similarly impressive results. A study of a bird realised £134,500 ($223,632), making a 647.2% increase on its £18,000 high estimate.

This was followed by a portrait of a boy, with a letter to Felicity in the corner. Valued at £20,000, it made £122,500 ($203,680) - a 512.5% increase on estimate. A portrait of Hellaby made £32,500 ($54,032), bringing the total price of the collection to £412,000 ($685,028).

The auction will be followed by Bonhams' sale of another letter written by Freud to a student admirer, which details his artistic aims, on March 19.

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