THE original sketches for the landmark bridge outside Balmoral Castle by the engineer Isambard Kingdom Brunel will go on show for the first time this weekend.

Brunel was commissioned to design the bridge across the River Dee by Queen Victoria's husband Prince Albert after they bought the estate in 1848.

The original 150-year-old Brunel sketches feature in his large Sketchbook No 8, and show two possible designs for the bridge.

The first, which was rejected, looks like a smaller version of his famous Royal Albert Bridge over the River Tamar on the border between Cornwall and Devon which was constructed between 1852 and 1859.

The chosen option is a wrought iron girder bridge.

The sketches are dated November 18, 1854 and the bridge was subsequently built between 1856 and 1857.

Brunel's original Sketchbook No 8 has been loaned for the occasion by the University of Bristol Special Collection.

The exhibition in Balmoral Castle, which opens to the public on Saturday, has been arranged to mark the bicentenaryofthebirthofBruneland to recognise him as the designer of Balmoral Bridge.

Aberdeenshire Council will unveil a plaque on the bridge which it owns later in the year.

Donald Macpherson, Aberdeenshire council's principal bridges engineer said: "The bridge has stood the test of time."