It will be transmitted on Channel 4 at 3pm - the same time as Her Majesty on BBC1 and ITV.
"Before there was just one Royal Family, you know, plodding along. Now you have a choice: the official one and mine. Classic Royal and New Royal Lite," she will say, distancing herself from the stuffy offering on the other side.
Sitting in front of a Christmas tree, skeleton in the corner, and surrounded by photos of her absent children, the lonely Princess, who will have altered her appearance again to look like Rory Bremner, the comedian, will appeal afresh to the hearts of the nation.
The down-cast eyes and winsome half-smile will be used once more to devastating effect. "You can take me out of the Royal Family, but you can't take the Royal Family out of me," will be part of her message. Diana will allude to the pressures she faces. "Take the Budget - the Daily Mirror got the whole thing the day before and didn't run it. Now if I'd been seen in a Range Rover down a slip road with Kenneth Clarke, I think they would have found a way to run that."
Most people will stick to the Queen. This year, though, one family, on holiday at Sandringham, could be forgiven for watching Channel 4.Reuse content