Jeremy Piven's not-quite mirror image playing Mr Selfridge
Mr Selfridge star Jeremy Piven was shocked to come face to face with himself as an old man - and see "more wrinkles than an English bulldog".
Piven, who plays Harry Selfridge, will finish the fourth and final series by taking the narrative up to the department store magnate's death at the age of 89.
The former Entourage star said: "Our entire make-up team is just so brilliant. To look up suddenly after they're finished and see that they've aged you 40 years - looking into the mirror is shocking.
"I'm incredibly vain and in total denial of my age, so for me it's not fun. It'll be like, suddenly you look in the mirror and suddenly you're a Shar Pei, and you have more wrinkles than an English bulldog."
Mr Selfridge is loosely based on the real-life story of Harry Selfridge, an American who founded the London department store. In later life he lost much of his fortune.
Piven said: "We are trying to be as true to life as possible, but at the same time we do take dramatic license.
"That's what's been a fun journey about this entire process, and it's not a biopic obviously, so we don't have to make sure we get every single detail right - but we're trying to be as authentic as possible."
He added: "We are going to show Harry at the end of his life, when he's much, much older in 1947. Wandering around his store as he did, and taking it all in and ultimately being kicked out of his own store.
"It's tragic. You get to see the entirety of someone's life and it's just been this gift to be able to be here and play him."
The series will start in the roaring twenties, when Harry becomes embroiled with the Dolly sisters - twin performers played by Emma Hamilton and Zoe Richard. By encouraging his gambling and spending, they contributed to his fall from grace.
Piven, 50, said: " I feel like Harry was born for the 1920s. It was just such a celebration that he loved, the energy and obviously he falls for the Dolly sisters.
"It was interesting. The first woman that he falls for in the series is Ellen Love, and she's a performer and an artist. And there's something about artists that - I think that Harry fancies himself as an artist as well and the retail is his theatre.
"But here he is falling for the Dolly sisters, and there's something about artists and performers that is so alluring to him."
Mr Selfridge began in 2013, but Piven said viewers could expect the best series so far.
He said: "This year, to me, feels like the best year. Everything we've done is now coming into fruition, and I think it's the best way to show how the end occurs. His demise.
"For instance, we've shot everything statically - the cameras are on sticks, as we say. And now, everything is movement. As the 20s did. So it's more immediate, it has more energy and pace and the stakes are much higher in the entire episode. They're not afraid to get really dark.
"So I'm just as excited about this season, as I have been about any season I've done in my life."
:: The final series of Mr Selfridge will begin on ITV on Friday, January 8.