Anthony Hopkins in a scene from Westworld. Picture: John P. Johnson/HBO via AP

The 78-year-old actor plays Dr Robert Ford in the show about a futuristic theme park populated by artificial beings.

And fans couldn’t believe their eyes when a flashback scene featured a much younger version of Hopkins in the third and most recent episode which aired yesterday on Foxtel in Australia.

Here’s what Hopkins normally looks like in the show:

Anthony Hopkins in Westworld. Picture: HBOSource:Supplied

And here’s what he looked like in the flashback scene:

A digitally de-aged Anthony Hopkins in Westworld. Picture: HBOSource:Supplied

And just for fun, here’s what Anthony Hopkins actually looked like in real life in 1969:

Anthony Hopkins in a publicity portrait for The Looking Glass War in 1969.Source:Getty Images

Fans took to Twitter to express their amazement at the flashback scene:

So how did they do it? Westworld’s visual-effects supervisor explained the process to Thrillist.

“We took a scan of Sir Tony and used that as our base,” Jay Worth said, “and then used a ton of photography and reference to figure out what we wanted him to look like”.

Once they’d created a CG version of Hopkins’ face, they transferred it onto the body of a stand-in.

Pretty cool huh?