His omission has nothing to do with plot lines, but instead is due to Sheldon Cooper’s (played by Jim Parsons) amazing memory.
Executive producers Bill Prady, Steven Molaro and Steve Holland were quick to quash rumours of a younger Leonard in the spin-off Young Sheldon.
Molaro told TV Insider: “With Sheldon’s eidetic memory, it makes it tough for him not to know when these things happen.”
They suggest that it would be unrealistic that there would be no mention of a younger Leonard and Sheldon relationship in The Big Bang Theory and that Sheldon has not remembered Leonard, given his memory.
An eidetic memory allows a person to vividly see a scene in their mind, even if they have only seen it briefly.
It would not make sense for producers to introduce a young Leonard because there would have been mention of it in The Big Bang Theory.
Young Sheldon covers Sheldon’s earlier years and shows how the quirky character developed into the man fans love in the CBS hit show.
Producer Prady has also revealed that the season 12 finale is still unfinished and they are still working on how to end the long-running series.
He said: “There are still pieces of the finale we have to figure out. We know some of the ‘what’. We don’t know all of the ‘how’.
“There’s a lot of talk about wanting to feel that the gang’s world will continue as viewers know it to be. Of all the feelings we’ve talked about that’s one that we all like.”
Penny Hofstadter star Kaley Cuoco agrees and has previously admitted that she just wants the finale to bring together the best of the show and give it the ending it deserves.
She said: “It’s going to be a surprise to all of us. Everyone is struggling to let go of this show, even the writers.
“I know that we’re all going to freak out reading that final episode. I hope that whatever loose ends they felt they needed to tie up will be tied up.
“I’m sure they want to see where all these characters end up, and I think the writers don’t want to leave some sort of ending.
“They want these characters to live on in people’s minds and hearts, so it’s going to have to be written in a very special way.”
She also revealed that there will not be a live audience for the series finale, unlike in previous seasons of the show.
She told E!News: “We’re actually going to pre-shoot the whole thing, so we’ll have shot it, and then we will have an audience taping. That was probably because they knew I’d be crying the entire time.
“So we still want the audience experience. We’re gonna still do the audience, but we will have taped it and shot it beforehand, so if the tears come unexpectedly, then that’s just what’s going to happen, because I guarantee you it’s going to happen.”
Fans will have to wait to find out what happens in the series finale in what are expected to be emotional scenes.
The Big Bang Theory airs Thursdays on CBS and in the UK on E4.