As discussions raged through the week, Prime Minister Tony Blair’s office worked alongside Buckingham Palace courtiers to plan and prepare for the funeral.

The princes’ uncle, Charles, 9th Earl Spencer, called the walk a “tunnel of grief” and told PEOPLE and The Story of Diana on NBC he didn’t believe that “tiny” Harry should have made the grueling walk.

“I was just so worried — what a trauma for a little chap to walk behind his mum’s body,” Spencer said. “It’s just awful. And, actually, I tried to stop that happening, to be honest.”

Blair’s aide Anji Hunter recalls in the BBC documentary that she made “an intervention on that — I thought, ‘How can he, [at] 12 walk, behind his mother’s coffin?’” But Hunter says she found it “astonishing and so moving” to see the boys undertake the task.

Meanwhile, Blair’s spokesman Alastair Campbell tells the documentary, “There was doubt until the final day as to whether the boys would feel able to do it, up to do it, whether they should do it.”

Diana, 7 Days airs on NBC on September 1.