In 2019, they opted for a dramatically different, spectacle-free celebration in Canada. And that would have been that, both events consigned to royal history and the Getty photo archives if it wasn't for a series of photos that have been posted over the last day or so by the royal family which have brought renewed focus on events that took place at Sandringham in December 2019.
Sunday was both Prince William's 38th birthday and Father's Day in the UK. The official Cambridge Instagram and Twitter accounts promptly put out two (and later a third) shot of the royal with his three children, all jovially gambolling across a perfect lawn.
Things got particularly interesting when it came to Prince Charles' official account, @ClarenceHouse. Firstly, to mark Father's Day, they shared a charming black and white image of the Queen, Prince Philip, a young Charles and a baby Princess Anne along with a bizarrely old image of Charles, William and Harry taken at a 2004 polo game.
Secondly, to mark William's birthday, a truly cockle-warming shot of Charles and William taken in December 2019 at Sandringham.
It is worth pointing out that for Harry's 35th birthday last year, Clarence House included an image that also featured William. This time, for William's big day, they only posted a single shot of Charles and William.
To borrow some of the sort LA-worthy lingo Harry should be brushing up on, there is a lot to unpack here.
The black and white retro shot is par for the predictable course. Nothing gets those likes and retweets like a suave, vintage Prince Philip displaying a modicum of paternal warmth. (Let's be clear: he was a bit of a dish back in the day.)
Next, the shot of Charles, William and Harry which was taken 16 years ago and which seems like a very odd choice. In a nutshell: Why? Harking back to the peaceful days of yore (and the days when the younger Princes had full, wonderful heads of hair) only serves as a reminder of how dramatically that dynamic has reportedly changed.
And then we get to the real clanger here: The birthday shot of Charles and William. This is unlike anything we have seen before from the royal family. Yes, in recent years the images put out by all the royal houses have got far less formal and far more personal. (Look no further than the image of Prince Charles hugging a baby Prince Louis.) But this picture, taken by Kate, Duchess of Cambridge, is truly intimate, offering a unique glimpse of a sort of private and tactile Windsor affection that is wholly unprecedented.
While it might tug at the heartstrings, what is even more interesting is where and when this photo was taken: December 2019 at Sandringham. The symbolism, whether intended or not, of both the location – Sandringham is the bosom of royal life – and the timing – when the Sussexes had left to the UK for a sabbatical – are particularly noteworthy.
The contrast between where the brothers were and what they were doing at this particular moment in time is marked. In December, Harry was thousands of kilometres away, cooped up in a borrowed mansion and reportedly already planning his withdrawal from the royal fold. Meanwhile, Charles and William were out enjoying a stomp across the moors, all smiles, hugs and jollity; some rugged father-son tweedy bonding time while ensconced in the royal bosom.
And that's the issue here. Whether accidental or not (and I find it hard to see why Clarence House would want to draw the public's attention to it), this birthday photo only highlights Harry's literal and figurative distance and isolation from his family. Whatever the intention, the selection of images chosen by Charles' people for both Father's Day and William's birthday all serve as an uncomfortable reminder of the chasm that currently exists between Harry and his family.
Given this is a man whose incredible capacity for warmth and love has time and again drawn comparisons with his mother, Diana, Princess of Wales, it is heart-rending to see the schism between him and his loved ones so glaringly on display.
There are no reports or details as of yet about what Harry did to mark his second Father's Day as a dad. (The Sussexes have yet to launch their new Instagram presence given they are no longer able to brand themselves as Sussex Royal.) No matter, I hope there were just as many hugs and just as much love for Harry in the LA sunshine and that, in years to come, there will be a day a third cheeky Wales boy joins his family for a tweedy Sandringham walk.
• Daniela Elser is a royal expert and writer with more than 15 years experience working with a number of Australia's leading media titles.