"Berline" is a prequel to the popular "Money Heist" series
"Berlin" is a prequel to the popular "Money Heist" series featuring Pedro Alonso. AFP

Two years after the end of the Netflix hit "Money Heist", which won millions of fans around the world, one of its main characters, "Berlin", returns to the small screen later this month with a spin-off series.

Although the Machiavellian criminal mastermind quickly charmed viewers, he died early on in the Spanish-language five-season thriller but remained very present thanks to multiple flashbacks.

And now he'll be back December 29 with an eight-episode prequel called "Berlin" in which the namesake gentleman criminal recruits a band of talented misfits to rob one of Paris's top auction houses.

In "Money Heist", or "La Casa de Papel" in Spanish, Berlin took centre stage as a mesmerising if manipulative sociopath with savage and unpredictable turns, but also a touching and endearing side.

Such was the fascination with his character that the Netflix production team kept him present long after his death in what was a challenge for Pedro Alonso, the Spanish actor playing the part.

Alonso warned the producers that he did not know if he was "capable of sustaining a character only in the past", especially one "who based his strength on danger, on the unpredictable, the unexpected", the actor told AFP in an interview.

"It's true that when you portray a character that works well, many people make this crazy switch in their head, so no matter what you say (off set), it's always Berlin who's talking!"

"But I can't do anything about that, and I don't want to anyway," he said.

Now 52, Alonso says playing Berlin, a "perverse, shady and difficult character, really got inside of me".

"Is the Berlin brand strong? Of course it is," he says.

And the eight episodes of the new prequel are only going to strengthen that.

"All the characters that I portray are partly me, which is to say that how I portray this character is in line with who I am," he said.

"Of course I have a bit of Berlin in me, but I've also got part of another character in me who I played this year, a father who is not an Alpha male and is an alcoholic."

Alonso says he is not an actor who is bent on "playing a totally different character every time".

On the other hand, he did hesitate before embarking on this new project following the enormous success of "Money Heist", Netflix's first non-English-language global hit, whose first season racked up close to 100 million views.

"When they brought up the idea of doing it, I asked them for some time to think. And it wasn't to think about the character himself but about the exposure of being involved in such a huge phenomenon as this," he said.

"At that point, it was a question of: do I really want to keep swimming in such exposed waters?"

The new series picks up the heist theme with a new mission in the Paris catacombs that Alonso said involves "more comedy and romantic comedy" -- and a new love interest for Berlin.

Asked about his slightly husky voice, whose varied tone and tempo is one of Berlin's seductive charms, Alonso starts laughing: "I've no idea what you're talking about," he grins.

"One time I heard Jose Sacristan, an actor I respect very much, saying: 'When you're 20, you have the face you've been given but when you're 50 your face reflects everything you've experienced in life'."

"So I guess in the same way, your voice develops as a result of what you've been through."

For him, "Money Heist" had certain uniquely Spanish elements that made it stand out.

"It has something to do with the emotional warmth of the characters, a type of resonance in their emotional, sentimental and even physical aspects which goes beyond what you would imagine in Anglo-Saxon heist films," he says.

"There is a certain effervescence of feeling."