Watch: Adil Ray questions Princess Diana funeral protocol for William and Harry.
Speaking on Good Morning Britain on the 25th anniversary of Diana's death in Paris, Ray reflected on the events and aftermath of her death and funeral.
Ray said: "Every time I see that scene of the sons walking behind the coffin I think 'Why was that allowed?' It’s a terrible thing for them to have to do, really."
The Citizen Khan actor went on to say: "For those of us who have lost loved ones in our lives, imagine having to do that. It’s just absolutely heartbreaking."
One of the most famous moments from Diana's funeral is of her two sons, then aged 15 and 12, walking behind her coffin with their father Prince Charles.
It has long been considered a controversial choice by the Royal Family who were criticised for putting her sons prominently in the spotlight.
Princess Diana died on 31 August in 1997 after being involved in a car crash in Paris. Her partner Dodi Fayed also died in the incident as did their driver Henri Paul.
Last year, on the anniversary of their mother's death, William and Harry got together to unveil a statue of the late Princess at Kensington Palace.
At the time, they said in a joint statement: "We remember her love, strength and character. Qualities that made her a force for good around the world, changing countless lives for the better."
Prince Harry has previously criticised the Royal Family for being unwilling to speak about Diana's death and his struggles with grief.
Harry said that he drank excessively and took drugs to try and deal with the death of his mother at a young age.