This is from the movie-'Seven Years in Tibet'(based on an autobiographical book with the same title written by the person on whom the movie is based.) A brief gist of the plot:-Austrians Heinrich Harrer (played by Brad Pitt) and Peter Aufschnaiter(played by David Thewlis) are mountaineering in British India in an area that is now Pakistan. When World War II begins in 1939, their German citizenship results in their imprisonment by the British in a POW camp in Dehradun in the Himalayan foothills, in the present-day Indian state of Uttarakhand. At that time Harrer's pregnant wife, Ingrid, sends him divorce papers from Austria.The letter also states that when their son is old enough,Ingrid will tell him that his father got lost in the Himalayas and died.In 1944, Harrer and Aufschnaiter escape the prison, and cross the border into Tibet, traversing the treacherous high plateau. While in Tibet, after initially being ordered to return to India, they are welcomed at the holy city of Lhasa, and become absorbed into an unfamiliar way of life. Harrer is introduced to the 14th Dalai Lama, who is still a boy, and becomes one of his tutors. During their time together, Heinrich becomes a close friend to the young spiritual leader. Harrer and Aufschnaiter stay in the country until the Chinese military campaign in 1950.

When Heinrich Harrer was missing his son while on his expedition,Peter Aufschnaiter suggested to him that he should write a letter to his son.It was during that time that Heinrich Harrer wrote this letter to his son.