ONCE Streatlam Castle was the home of the tenth richest man in England. He filled it with some of his most prized and personal possessions, and he used its parkland to breed some of the finest racehorses of the Victorian era.

The castle, though, was blown up by the Army in 1959, and today dotted around the parkland are lots of little bits that hint at once was the home of the founders of the Bowes Museum: there’s an orangery, an archway, a monument to a Derby winner, a collection of now mature exotic trees, a culverted stream, a leg-mangling mantrap…

All of this is pieced back together in an exhibition which opens at the museum on the edge of Barnard Castle today. It brings the lost castle of John and Josephine Bowes back to life, and at its centre is a pair of intricate models which show the extraordinary scale of their home and how it once sat in its manicured Teesdale parkland.

Streatlam Castle, to the north-east of Barney, was the home of the Bowes family from the early 14th Century, and its ups and downs mirrored their ups and downs. For instance, during the Rising of the North in 1569, Sir George Bowes backed Queen Elizabeth, but his castle was plundered, stripped even of its 40 feather beds. The Queen did reward him for his loyalty, but not regally enough for him to be able to restore his despoiled home and he died in 1580 of a broken heart. His ghost still haunts the lonely glen to this today.

However, his great-grandson, Sir William, married the Blakiston heiress whose family owned Gibside and the great coal seams beneath it. The Boweses were back in the money – and the medieval castle was reshaped once more around 1720.

Two generations later, and the Bowes heiress, Mary Eleanor, married the ninth Earl of Strathmore to create the Bowes Lyon name. He died after nine years of marriage leaving Mary Eleanor the wealthiest heiress in all Europe.

But she chose badly. Her second husband was a notorious rogue, Andrew Robinson Stoney Bowes, who beat her up, raped her servants and misappropriated her fortune. In 1785, when she finally filed for divorce, he held her hostage at gunpoint in the castle to try to intimidate her into dropping the separation.

Local people, understandably worried for the countess’ safety, gathered outside with a view to storming Streatlam and setting her free. But before they could act, Stoney Bowes tied her onto a horseback and set off on a crazy ride across the snow-covered Durham moors.

Eventually, Mary Eleanor saw off her husband, but she left Streatlam “deserted and fast falling into decay and ruin”.

Her oldest son, John, became the tenth Earl of Strathmore, inherited the castle and put it on an upward curve once more. His passion was racehorses, but his great love was the humble daughter of a gardener from nearby Stainton.

Her name was Mary Milner and one of the highlights of the exhibition is a new portrait of her found in the private quarters at Glamis Castle. In 1811, she gave birth to the earl’s son, John.

Mary and the 10th Earl were an item for many years, but it was only on his deathbed in 1820 that they regularised their relationship and got married, probably in an attempt to make the boy legitimate.

The earl died 16 hours later, and nine-year-old John inherited Streatlam but, after a bitter court battle, he was allowed to keep the Durham lands but he lost his Scottish title due to his illegitimacy.

“As soon as he inherited the castle, there was a blizzard of plans to improve it,” says Jonathan Peacock, who has curated the exhibition. “It was a rather plain and unadorned building and he stuck the portico and cupolas on it and turned it from a castle into a mansion.”

John’s coal-rich County Durham lands brought him an annual income of £3m in today’s values. Then came proceeds from his horseracing: in 1843, Cotherstone, bred at Streatlam, won the Derby – not only did John collect the £4,250 prize but he had bets worth at least £21,000 riding on the race. That afternoon, he earned as much from the horses as he did from his land in a year, although he was forced to lie low in France for a year to avoid being prosecuted over an allegedly underhand gambling practice.

John’s most famous horse was West Australian, which in 1853 became the first horse ever to win the Triple Crown – the 2,000 Guineas, the Derby and the St Leger – in the same season. Only 14 horses have matched West Australian’s achievement, and when it died in 1870 in Paris (it was then owned by Napoleon III), a monument in its honour was erected at Streatlam.

“John Bowes was one of the greatest horsebreeders this country has ever known – for instance, he was one of only five men to win the Derby four times,” says Jonathan.

Paris exerted an increasing hold on John during his thirties, as it allowed him to escape the conventionalities of Durham and the controversy of his illegitimacy. He bought a theatre and then a chateau and in 1852, he married an actress, Josephine Benoite Coffin-Chevalier, 13 years his junior. They began buying artistic artefacts, storing them in the chateau, with the madcap idea of some day establishing a museum.

“John clearly loved Streatlam Castle – he had been brought up there and it was always home to him, but he spent very little time living there,” says Jonathan. “He was a very absentee landlord. Even when he was living in Paris, he was writing two or three letters a day to his agent, Ralph Dent, with copious instructions about the castle.”

Many of those letters were about the Streatlam parkland. John had tens of thousands of tons of soil moved to culvert a beck to improve the approach to his castle. In 1864, he planted a pinetum of 153 rare trees, mainly from America, of which 92 survive, and one day in 1883, he decided that a pair of 25ft tall sycamores were too close to his drive, so he had them moved. They weighed eight tons each, and team of horses dragged them 30ft to their new position along a specially dug trench.

John filled his castle with his personal collection of art and furniture, which he had either inherited or bought pre-Josephine. His collection with Josephine was very different, and was always intended for the museum.

In 1860, they sold the chateau on the banks of the Seine and began to decamp to Streatlam, to establish the museum. Their move was aided by them having a personal halt, called Broomielaw after another of John’s successful horses, in the middle of nowhere on the Darlington to Barnard Castle railway line.

However, their dozen or so favourite orange trees sailed from Paris in specially-built packing cases on a barge to Middlesbrough. From there, they were pulled by horses along the roads to Streatlam, a crew of men lopping off the branches of overhanging trees along the A67 to ensure their safe arrival.

The heated orangery that John created for them is one of the few pieces that survives at Streatlam.

Sadly neither Josephine nor John lived long enough to see their museum, in a giant French chateau, open in 1892, although the exhibition about their British castle is one of a series of events celebrating the museum’s 125th anniversary (the full story of the Bowes Museum’s 125th anniversary was told in Memories 331).

Josephine died in 1874 and John died in 1885, and after them, the Bowes-Lyon family found that Streatlam was one castle too many. It was sold in 1922, and the new owner striped out everything saleable – even the lead from the roof – and then abandoned it. During the Second World War, it was occupied by the Army, which did not improve its condition, and finally, on March 29, 1959, the Territorial Army was allowed to do an exercise involving dynamite on the site.

And so the castle that had been the Bowes family since 1310 disappeared in a rumble of explosives, a puff of smoke and a cloud of dust.

Now only tantalising bits and pieces remain amid the private parkland.

“The exhibition has allowed us to re-evaluate what remains, and in researching it, we’ve learned so much more about John and Josephine Bowes and the extraordinary collection they have left us in the museum,” says Jonathan.

Although Jonathan is delighted with the paintings that have come from afar and the castle models, which have been made by the skilled fingers of Martin Saville, another of his favourite exhibits is the leg-mangling iron mantrap which was found in the parkland.

“It wasn’t technically illegal in John Bowes’ time, but I don’t think he used it,” says Jonathan. “However, poaching was a real problem at Streatlam, so it is all part of the story.”

The Streatlam Castle exhibition runs until March 11, 2018, after which it transfers to Glamis Castle, the Bowes Lyon home where the 19th Earl of Strathmore currently lives.