In looking back, a serious gaffe has been spotted by fans that had been lost in the many The Big Bang Theory episodes.
It involves Howard Wolowitz (played by Simon Helberg) and Raj Koothrappali and a pair of female models in the CBS sitcom.
They head to the house of America’s Next Top Model and bump into Analeigh Tipton and Samantha Potter from the real-life show.
In somewhat outdated scenes, the pair sneak into the house under the disguise of fixing the television.
Then, flash forward seven seasons and the pair come face-to-face with Analeigh again as she makes her second cameo.
However, the scene goes totally unacknowledged and it appears bosses forgot she had been in the show before.
In season seven, the duo helped Sheldon Cooper (Jim Parsons) devise a questionnaire for a new girlfriend after he briefly separated from long-term girlfriend Amy Farrah Fowler (Mayim Bialik).
With Amy dating David Gibbs (Stephen Merchant), Sheldon decided he would move on as well and in typical Sheldon fashion created a knowledge-based quiz to find a new date.
Ironically, it was Analeigh who won a date with Sheldon and she came to his flat to meet Sheldon and claim her date.
Although giving her name as Vanessa, it is still shocking she as not recognised and instead was sent packing after arriving too late.
This is not the first issue fans have spotted about the show whilst looking back at previous seasons.
In looking back through the 12 seasons of the show, one Reddit fan has noticed a fashion choice by Penny (played by Kaley Cuoco) is repeated when an important event is taking place.
Completing a huge full circle moment for Penny, Reddit user thegirlwholaughed revealed she wears a light blue T-shirt in the final episode that she is also seen wearing in the first ever episode.
The top has a purple flower design on one side and this is what made the fan realise it was the exact same one worn in season one.
It represents an important moment in Penny’s life as it is in the first ever episode that she meets future husband Leonard Hofstadter (Johnny Galecki) and his best friend Sheldon Cooper (Jim Parsons).
The trio’s meeting has shaped the success of the show and they have taken fans on their 12 seasons’ journey.
Meanwhile, Kaley Cuoco, who plays Penny Hofstadter, revealed on The Late Show with Stephen Colbert how hard it was for the cast to keep the ending a secret from fans.
Sheldon star Jim also added: “I was talking to one of the writers and he was like, ‘I’m nervous!’
“And I was like, ‘Well, you can’t get it wrong because it’s yours, you’ve been writing it all this time.’
“I said, ‘Look at it this way: You can’t get it right. It’s a series finale. Someone’s going to hate it’.”
The Big Bang Theory season 12 is available on CBS and All4.