The Duchess of Cambridge borrows diamond necklace from the Queen to attend the Portrait Gala 2014 at the National Portrait Gallery, London

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Duchess of Cambridge visits National Portrait Gallery, home of little-known Middleton family paintings

The Duchess of Cambridge borrows diamond necklace from the Queen to attend the Portrait Gala 2014 at the National Portrait Gallery, London

As patron of the National Portrait Gallery, it is to be expected that the Duchess of Cambridge’s own image is hung on its walls.

But few will know the gallery also holds nearly 20 portraits of two of her distant relatives, Dr James and Harriet Martineau.

The notable figures, going back six generations of her father’s side of the family, have portraits stored in the vast collection of the NPG.

Wearing a diamond necklace borrowed from the Queen with a dress by Jenny Packham, the Duchess paid visit to the gallery on Tuesday evening as her first Royal engagement of the year.

The little-known works were noticed by Australian historian Michael Reed, who has previously mapped the Duchess’ family tree, alerting the palace to her great-great-grandfather Francis Martineau Lupton.

Francis, a wealthy mill owner, was in turn the great-nephew of Dr James Martineau, a friend of Queen Victoria, and Harriet Martineau, the noted writer.

Miss Martineau, born in 1802, is remembered for her campaign for women's rights and argued for an improvement in women's education, so that "marriage need not be their only object in life".

The NPG currently holds ten images of James Martineau is its collection, including pencil drawings, plaster casts and prints; none of which are on display currently.

It holds a further eight of Harriet Martineau, of which one – an oil on canvas by Richard Evans – is available to the public in the Ladies Drawing Room at Bodelwyddan Castle, Wales.

A spokesman for the gallery confirmed the portraits were in the collection, but said curators had not confirmed the link to the Duchess independently.

The Duchess’ own portrait, by Paul Emsley, is on display at the London gallery, after being unveiled in 2012.

She has now attended the NPG’s Gala with guests including photographer David Bailey, Olympic rowing gold medallist Katherine Grainger and British artists Grayson Perry and Jonathan Yeo.

The Duchess, who recently returned from holiday on the island of Mustique with her family and six-month-old son Prince George, viewed hand-written Pen Portraits and the Mystery Portrait Postcards on display, aimed at raising money for the gallery.

The "pen portraits", described as exclusive stories, descriptions and commentaries about a chosen painting in the gallery's collection, include offerings by Hilary Mantel, Dame Jacqueline Wilson, A S Byatt, Ben Okri, Sir Roy Strong, and Sir David Hare.

Funds raised will support the gallery's work to deliver exhibitions and displays and carry out research, with some going towards the acquisition of new portraits.

This article originally appeared in :  Duchess of Cambridge visits National Portrait Gallery, home of little-known Middleton family paintings | telegraph.co.uk | By Hannah Furness9:20PM GMT 11 Feb 2014