At the beginning of series three of The Crown, we see the Queen surveying two reproductions of her profile.
One silhouette belongs to actress Claire Foy, the other to Olivia Colman who has now replaced her in the role. "A great many changes," says the Queen, looking from young to old, old to young.
"There we are. Age is rarely kind to anyone. Nothing one can do about it. One just has to get on with it."
And get on with it The Crown certainly does. Colman inhabits the part so completely that, just a few minutes in, memories of Foy's award winning performance start to fade.
Of course, it's not the only significant piece of recasting in Peter Morgan's drama, which moves the action forward to the years 1964-1977.
Tobias Menzies has replaced Matt Smith as the Duke of Edinburgh, Vanessa Kirby has now transformed into Helena Bonham Carter as Princess Margaret, with Ben Daniels taking over the role of Lord Snowdon (previously Matthew Goode).
This is a challenging transition for both actors and audience alike. As the bright-eyed Queen and Duke of Edinburgh, torn between youthful naïveté and the crippling duties of high office, Foy and Smith were both believable and dashing.
Kirby, as Elizabeth's forlorn younger sister, was perhaps even better, her Margaret a flickering star forced into the shadows by her station.
"For the first few days, it felt like I was trying to be Claire," Colman told The Telegraph earlier this year. "[She] was just so brilliant that it's quite a pressure to take over from her. But then you've got to go, 'F--- it, I've been given the job, I've just got to do it."'
Colman also revealed that the director, Benjamin Caron, gave her a concealed earpiece through which she would listen to the neutral tones of the Shipping Forecast, to help her suppress her emotions in some of the more distressing scenes, such as the Queen's visit to Aberfan following the 1966 disaster.
This, she said, helped her to reproduce the Queen's famous stoicism. And, indeed, Colman does a great job of conveying the Queen's sober devotion to the job. I personally feel, however, that Menzies and Bonham Carter pale in comparison to their predecessors.
The Outlander star's Prince Philip looks and sounds like the real Duke of Edinburgh, but he doesn't boil beneath the surface as Smith's Philip did. Meanwhile, Bonham Carter, reimagining Margaret's hunger for the spotlight almost as an addiction, invites awe rather than empathy.
It is even more challenging for actors and actresses when their character is played by two people in the same film. Meryl Streep made for a convincing Margaret Thatcher in the 2011 biopic The Iron Lady (and indeed won an Oscar for it).
Yet, the actress's nuanced performance was undermined by flashbacks to the younger Margaret as portrayed rather more broadly by Alexandra Roach, then 28.
There are exceptions. Who could forget the brilliant dual performances of Saoirse Ronan and Romola Garai as the tortured Bryony in the big-screen adaptation of Ian McEwan's Atonement?
The elder actress - Garai - poignantly displayed the residual guilt that stemmed from her younger character's fatal moment of foolishness.
Colman's impressive debut in The Crown is a reminder, moreover, that a world-class performer can instantly make a character their own. That was also the logic applied by Jonathan Demme when casting the part of Hannibal Lecter in The Silence of the Lambs.
Future Succession star Brian Cox was a fantastic Lecter in Michael Mann's Manhunter (1986). Demme could have played it safe and had him back. But instead he took a risk and gave the part to Anthony Hopkins.
The moment Hopkins appeared on screen it was impossible to think of anyone as Lecter ever again. (The actor himself has never made any secret of the relish with which he took on the role and has said he knew instinctively how to play it.)
It may seem like strange praise to compare Colman's performance to a maniac in a mask. But it's no stretch to imagine that her Elizabeth II will come to be regarded as every bit as definitive as Hopkins's Hannibal.
The Crown is on Netflix now