In the first episode of Joey, Joey Tribbianni says "I was happy in New York and I tried to keep everything the same but things kept changing. All of my friends got married and had kids and moved on." At another point later in the series, Joey says to Alex "I've only said I love you to one woman and she was pregnant with my best friend's baby and they ended up together".
Some people choose to believe that the above lines imply that Ross and Rachel remarried one another, others point out that considering their history and patterns this would be unlikely. In fact, Joey's statements are vague and can be interpreted in different ways:
- Ross and Rachel may have indeed stayed together for a long time after the series finale, and even remarried at some point. Some of the crew have stated they believed so. In "The Last One, Part 2" both Rachel and Ross stated that "this was it", and they wanted to make it work. It is possible that Joey's line "got married" referred to Ross and Rachel marrying each other, and "ended up together" referred to the point in time when Joey talked, a few months after "The Last One", rather than the day depicted in the last episode of the show. Unlike all previous times when Ross and Rachel got back together and broke shortly after, this time they are older, more mature and even have a child together. All this could, and should, encourage them to try harder than before.
- It is possible that Joey's line "got married" refers to Chandler, Monica and Phoebe, or he may have referred to Ross and Rachel's drunken wedding in Las Vegas. "Ended up together" may have referred to the day depicted in "The Last One, Part 2". The lack of understanding, the lack of respect, the lack of communication, and the lack of trust between Ross and Rachel, and the breaking up shortly after they get together, are patterns which repeat throughout the last 7 years of the show, and could possibly continue to repeat after "The Last One".
- Since Joey never clearly says "Rachel remarried Ross" (or vice versa), both Ross and Rachel may have married different people -- such a situation has already happened before in season 4 and 5, when Ross fell in love with Emily Waltham and married her, and at the same time Rachel proposed to Joshua Burgin and would have married him if he didn't freak out.
The lack of a reference -- both reliable and in-universe -- Rachel and Ross marrying each other after "The Last One, Part 2" or even staying together after the last scene, often cause speculations and disagreements among fans about what might have happened after the last episode. Until there are official episodes of a Friends continuation, this question cannot be answered.