Why Meghan Markle appears in Queen Elizabeth's documentary, but Kate Middleton doesn't.

Meghan Markle, the latest member of the royal family, takes a starring role in the Queen‘s new documentary.

Kate Middleton… Not so much.

The documentary, Queen of the World, will tell the story of how the Commonwealth has been a central focus and passion throughout Her Majesty’s life.

The preview shows the Duchess of Sussex reacting to her wedding dress for the first time – so it’s clear she’ll be making a major appearance – but Kate is no where to be seen.

Don’t worry, the Queen isn’t playing favourites. It’s all to do with the timing of filming.

It’s been a crazy year for the British royals – among the multiple royal weddings, we also had the birth of a prince.

The Duchess of Cambridge was heavily pregnant and on maternity leave following the birth of Prince Louis in April, when a lot of filming for the documentary was conducted.

The Commonwealth is the main feature of the film and CHOGM, the British meeting of the heads of government from the 53 Commonwealth nations in April, is a central element.

“Kate was largely out of action during the main filming,” an insider with the documentary told PEOPLE.

“CHOGM was a focal point and she was due to give birth any minute then.”

But thankfully, Kate will make small appearances. She just doesn’t have a major role and won’t be seen speaking to camera or in conversation like Meghan, Prince Harry and Prince William.

The doco covers events and receptions that she attended, so we’ll see her at these.

Prince Louis was born on April 23 and Kate has been taking some well deserved time off. She’s expected to remain on maternity leave until October.

Queen of the World premieres on ITV on September 25. It will air in Australia on Channel Seven, which has yet to advise its release date.