Declassified documents here about Osama bin Laden reveal that he was a dedicated family man who constantly worried about his four wives, 20 children and other relatives and who sometimes issued detailed instructions about how they should conduct themselves.

Bin Laden took minute interest in the marriage plans of his son Khalid to the daughter of a “martyred” Al Qaeda commander, and he exchanged a number of letters with the mother of the bride-to-be. Bin Laden excitedly talked about the impending nuptials “which our hearts have been looking forward to”.

Bin Laden corresponded at length with his son Hamza and with Hamza’s mother, Khairiah, who had spent around a decade in Iran under house arrest following the Taliban’s fall in neighbouring Afghanistan during the winter of 2001.

Hamza wrote a heart-stirring letter to bin Laden in 2009 in which he recalled how he had not seen his father since he was 13, eight years earlier: “My heart is sad from the long separation, yearning to meet with you … My eyes still remember the last time I saw you when you were under the olive tree and you gave each one of us Muslim prayer beads,” reveal documents translated from Arabic to English.

In 2010, the Iranians started releasing members of the bin Laden family who had been living in Iran. Bin Laden spent many hours writing letters to them and to his associates in Al Qaeda about how best he could reunite with them.

In a letter to his wife Khairiah, he wrote tenderly: “How long have I waited for your departure from Iran.”

Bin Laden was paranoid that the Iranians — who he said were “not to be trusted” — might insert electronic tracking devices into the belongings or even the bodies of his family as they left Iran.

He told Khairiah that if she had recently visited an “official dentist” in Iran for a filling that she would need to have the filling taken out before meeting with him as he worried a tracking device might have been inserted inside.

US intelligence officials have a theory that bin Laden might have been grooming Hamza eventually to succeed him at the helm of Al Qaeda because, he felt, the son’s relative youth would energise Al Qaeda’s base.

But Hamza never made it to his father’s hiding place in Abbottabad, the Pakistani garrison township in Khyber-Pakhtunkhwa province.

When the US SEALS raided bin Laden’s compound, they assumed Hamza would likely be one of the adult males living there, but he was not.

US intelligence officials say they do not know where Hamza, now in his late 20s, is today.