Money Heist fans have been fascinated with Alicia Sierra ever since she first appeared in the third season of the Netflix hit. Alicia is a tough, cold-hearted Inspector who will do what she has to complete a job and get the outcome she wants. She was last seen holding a gun to The Professor’s head in the season four finale thinking he is her enemy – but could he be her brother?

The ruthless Inspector has infuriated Money Heist fans as she was revealed to have tortured Rio (played by Miguel Herran) by burying him alive, starving him and keeping him in a tiny cell as she interrogated him about The Professor (Alvaro Morte). In season three, Alicia (Najwa Nimri) paraded Nairobi’s (Alba Flores) son Axel in front of the Bank of Spain which lead to the robber being shot in the chest. Her cold-heart and determination to take down the gang has now led fans of La Casa De Papel to consider she could be related to The Professor and Berlin (Pedro Alonso).

For a while, it was believed Alicia was actually Berlin’s wife Tatiana (Diana Gómez) however, season four clarified this wasn’t the case. Now fans think she is still linked to Berlin and The Professor but biologically, not romantically. While it appeared Alicia had the upper hand at the start of season four, she was quickly taken down a peg or two when The Professor exposed her chilling behaviour and how she tortured Rio.

Alicia subsequently lost her job and went out looking for revenge, finally finding The Professor’s bunker and holding a gun to his head ready to end the heist. But fans think Alicia could be stopped from killing him before it’s too late when it’s revealed they are related. Reddit user Tiffy00 theorised: “I disagree she’s Tatiana. Professor would have recognised her and she worked with Raquel.

“I thought that Professor, Berlin and Alicia are siblings! I have read this theory on YouTube comments too! It makes sense.

“The three of them are super intelligent, can predict other people’s next moves, are real bosses and love music.”

The fan went on to add: “Especially Berlin and Alicia have quite a same personality.

“They like to be admired and everyone to listen to them, they are funny, they always want to have the control and enjoy when other are in pain.

“Also Berlin wanted to kill Monica, although she was pregnant and Alicia used Axel to shoot Nairobi. So they don’t appreciate mother-child issues.

“Plus Berlin wanted to kill Rio and Alicia tortured him. They could be twins! Perhaps Alicia is a lost sister and Professor and she will find out and that’s why she will help him.”

The trio certainly share a number of traits as in the first two seasons, it was clear Berlin liked to be in control of the gang and the centre of attention – remember when he brought a camera crew into the Royal Mint for an interview?

The Professor always seems to know the police’s next move but several times, Alicia has guessed his plans and he’s been shocked by her intelligence. Could the trio really be siblings or is that too far fetched even for Money Heist? Well, lots of fans certainly think it’s a possibility with one replying: “The theory is super well thought out, but the soap-opera-ness would be too cringey I think.

“I mean the show is half telenovela, but this would be over the top, even for them.

“I feel like we’re putting too much emphasis on relating Sierra to Professor or Berlin, but it is most likely that she’s just a police officer who happens to hate their guts.

“I also kinda just want to see her not join the Professor’s cause, so I may be a little biased.”

Unfortunately due to the coronavirus pandemic it seems fans will be waiting a little longer for the next series as production was temporarily put on hold. However, a video released by Netflix Spain last week confirmed the cast would be heading back onto set very soon.