The only known photograph of the iceberg believed to have sunk the Titanic is to go on display in the UK for the first time.

The image is a key exhibit at Europe's biggest ever Titanic exhibition, which is being held in Dundee next month.

The sepia picture of the iceberg was one of a series taken by Stephan Rehorek on 20 April, 1912, six days after the disaster.

I also saw the bodies of the drowned and the wreckage from the ship. It was a dreadful sight.

Stephan Rehorek

It was bought by Titanic collector Henning Pfeifer, who is convinced of its significance.

Mr Rehorek was thought to have been a Czech sailor on board the German passenger steamer Bremen, which had been en route from Bremerhaven to New York but was diverted to the disaster area.

The crew was horrified to see more than 100 bodies of Titanic passengers and crew floating in the Atlantic.

However, the plan to recover bodies was changed when the Bremen captain heard that the US-registered Mackay-Bennett, which had been chartered for the purpose, was just two hours away.

Before the vessel left, Mr Rehorek took photographs of two icebergs in the area.

When he arrived in New York, he sent a postcard home, which was postmarked 25 April and which, for an unknown reason, referred to the Titanic as a Dutch vessel.

An iceberg picture was posted in Cherbourg

On the front was a souvenir picture of the Titanic and he wrote: "Dear Mother and Father. Best wishes from New York.

"I am sending you a picture of a Dutch fast ocean liner which sank on its maiden voyage.

"It was the biggest in the world. Two days away from New York it collided with an iceberg and the ship was severely damaged on one side.

"Almost 1600 people drowned and about 670 were rescued. I have a photograph of the iceberg and will send it to you.

"I also saw the bodies of the drowned and the wreckage from the ship. It was a dreadful sight."

Several weeks later Mr Rehorek got the photographs of the icebergs printed onto postcards and sent one to his parents from Cherbourg.

He wrote: "Dear Mother and Father. This card is a view of the iceberg that collided with and sank the Titanic liner. I will send a card to Josef too."

As soon as I looked at this one iceberg I knew I was holding a piece of history in my hand

Henning Pfeifer

The postcard sent to his brother Josef showed a souvenir picture of the Titanic.

He wrote: "Dear Josef. I am sending you, too, a postcard of the ship that sank. We were following about a thousand miles behind it.

"Next time you come home our parents will show you pictures of the icebergs which were photographed from our ship."

Mr Rehorek kept two other existing photographs, which showed another iceberg.

All of the pictures caught the attention of German journalist and Titanic enthusiast Henning Pfeifer in April 2000.

Mr Pfeifer bought them from a Czech postcard collector and gradually became convinced that one of the icebergs had struck the Titanic.

He said: "As soon as I looked at this one iceberg I knew I was holding a piece of history in my hand.

More than 1,500 people died on the Titanic

"I remembered reading evidence from the inquiry after the disaster when one survivor had described the iceberg as looking like the Rock of Gibraltar but a mirrored version.

This iceberg was just like it but it had a fresh break on one side."

Mr Pfeifer and Gunter Babler, from the Swiss Titanic Society, considered four factors when looking at the iceberg.

City of Discovery

These were its location, the age of the picture, a survivor's account of the appearance of the iceberg and the iceberg as it appeared in the picture with "a fresh break on one side and, importantly, an overhang which is consistent with that evidence".

The Dundee exhibition is being held to commemorate the 90th anniversary of the disaster that claimed almost 1600 lives and will run from 10 to 18 August at City Quay.

It has been organised by the Tayside branch of the Maritime Volunteer Service and backed by the Dundee City of Discovery Campaign.