Car Share viewers were left in dismay at the end of the second series when Kayleigh stepped out of John’s car and his life forever.
Fans even set up online petition demanding a conclusion to the series which gathered over 100,000 signatures.
Last year Peter Kay confirmed that the show would be back for one more episode.
Peter Kay said in 2017: “We were completely overwhelmed by the response and even though we've no plans to write a third series we knew we couldn't end the story there.”
Teasing the final episode this week, Peter said: "We always knew the second series would end that way and we thought people might be a bit miffed but never thought they would be so devastated.
"We decided to write another episode that hopefully gave the characters a resolve and I thought let's hold this back until the repeat of the second series.
"It was hard to keep it a secret after the reaction we got, but we never said that there wouldn't be any more Car Shares... we just said there wouldn't be a third series."
However co-star Sian Gibson suggested that there could be even more to come, saying: "Never say never!"
The new episode this Monday follows Car Share: Unscripted which saw John and Kayleigh home on their daily commute only the entire episode was completely improvised.
Peter said: "I think it’s always good to try and do something original and I couldn’t think of any other narrative comedies that have ever made a fully improvised episode.
Charlotte Moore, Director of BBC Content commented of the two specials last year: "I know it will be music to the ears of millions of fans of Peter Kay's joyous award winning comedy to hear that Kayleigh and John will be coming back for one last time with a very special finale episode in 2018."
Shane Allen, Controller Comedy Commissioning added: "Car Share has been the hit comedy of 2017 with audiences of over 11 million.
"This new finale is going to be the TV comedy equivalent of The Space Landing, ‘Who Shot J.R.?’ or The Olympics Opening Ceremony depending on how old you are”