The letter my mum left for us - moments before she was killed at Auschwitz

Vilma Grunwald with her sons John (left) and Frank (then known as Misa). 

Moments before she was gassed to death by the Nazis in July 1944, Vilma Grunwald gave a guard a letter for her husband and family who were also in the largest Nazi concentration camp, Auschwitz.

The guard passed it on to her husband Kurt, but for decades the couple's youngest son, Frank, was unable to to read the handwritten note.

Here, 75 years after the death camp was liberated, he tells Sky News how it felt to read the letter which is now on display to visitors at the United States Holocaust Memorial Museum:

My father, mother and older brother and I were sent to Auschwitz in December 1943.

A transport of around 5,000 inmates had arrived at the camp in September before us and we were part of the second batch of 5,000.

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We had no idea why we were there.

We were kept in a Czech family camp which was a ploy by the Nazis to show the International Red Cross that Czech Jews were being well looked after.

At the time, we had no idea why the family camp was even established because most of the time, when children arrived at the Auschwitz railway station, they were almost immediately killed in the gas chambers.

The International Red Cross never inspected Auschwitz so the Nazis gassed and killed most of the September transport.

This was in the March and April of 1944.

Then a few months later, they decided to make a selection from the second group which my family and I were in.

We all lined up in front of notorious SS doctor Josef Mengele, nicknamed the Angel of Death, who selected who would live or die.

My brother John, who was four years older than me, was handicapped and he was chosen to die.

And, because I was less than 12 years old, I was also put on death row. 

We were both standing in the line when one of the prisoners I had been working for as a messenger came over and quickly moved me into a group of older children.

He had saved my life.

But when my mother found out that John, who was 16, was going to be gassed, she decided to stay with him.

She could not bear the idea of him going into the gas chamber by himself.

About five days after the selection, she wrote a letter to my father, who had been moved to a medical camp because he was a physician.

She gave it to a guard and - despite the massive size of Auschwitz - he delivered it to my father.

There were between 30,000 and 40,000 guards in the camp and many of them were not SS.

Some of them were older military people in their 50s and 60s who had not been brainwashed by the Nazi regime.My father, mother and older brother and I were sent to Auschwitz in December 1943.

My mother, who was always a good judge of character, had picked the right person.

A few months later, Auschwitz was liberated, and I was reunited with my father - by this time I was in Austria and he was in Germany.

It was then he told me he had a letter from my mother, written to him shortly before she and my brother were taken on trucks to the gas chambers.

He told me it was a goodbye, a loving goodbye to him, and that my mother had wished him a good life.

I was only 12 years old at the time, so it was too painful to read and I pushed it to the back of my mind.

We lived in London for two years, and then moved to New York City in 1951.

My father practised medicine there and I went to the Pratt Institute and studied industrial design.

I didn't see the note until after my father died in 1967 and I was sorting out his possessions.

I had thought about it many times over the years and I was curious, but I knew it would be too depressing and upsetting to read.

I felt those 10 sentences, scribbled in pencil on paper she had found in the camp, were simply too closely linked to her death.

And when I did eventually read it, I found it really disturbing because I was immediately in her situation.

But I also amazed about how positive and how calm she was in the letter.

My mother's brave words lacked any anger or hatred towards the Nazis and instead was just so positive.

She was more interested in my father's life and in my life than in her own terrifying situation.

The letter, dated 11 July, 1944, read: "You, my only one, dearest, in isolation we are waiting for darkness.

"We considered the possibility of hiding but decided not to do it since we felt it would be hopeless.

"The famous trucks are already here and we are waiting for it to begin. I am completely calm.

"You - my only and dearest one, do not blame yourself for what happened, it was our destiny.

"We did what we could.

"Stay healthy and remember my words that time will heal - if not completely then at least partially.

"Take care of the little golden boy and don't spoil him too much with your love.

"Both of you - stay healthy, my dear ones. I will be thinking of you and Misa. Have a fabulous life, we must board the trucks.

"Into eternity, Vilma."

I kept the letter in a cupboard in my home here in Indianapolis for many years, not showing it to anyone.

Every few months I would take it and reread it.

Then one day, my wife, Barbara, saw it so I translated it for her from my mother's native Czechoslovakian.

I don't remember reading it to my two boys at the time, who are now in their 30s and 40s.

A few years ago I decided it was not doing me any good keeping it here.

I made copies of it and decided to give it to the US Holocaust Memorial Museum in Washington.

I never realised it was going to have the impact it has had.

I have had so many emails and letters both from people I know and people I don't.

The letter is so positive and so giving, yet also so sad, but what I want them to take away from it is that there were millions of other people like my mother.

People who never hurt anyone or wished anything bad on anyone, that were killed in those camps.

The museum has told me that it's the only artefact of all the hundreds of thousands they have - like shoes, clothing, personal belongings - that represents or resonates the full emotion and mental health of a prisoner just before their death.

I remember telling my wife that I was so concerned that, when I am not around, my mother will be forgotten.

Now, that the letter is on exhibit at the museum, she will not be.