Seán had always liked Mark, in fact he looked up to him. So there was one day when Mark found His channel and private messaged him on his twitter. Mark is the reason why Jack made his channel actually. Seán says that he admires the way that Mark made YouTube about the fans and not the numbers, and he follows that code just as much as he would. Even though they have known each other for a very long time now, Jack still looks up to Mark and cares deeply for him Their very first collaboration video was published on April 25th, 2014.

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This part is true 100%
The rest probably won't be since they are of course not together cannonally but it will still be as enjoyable as if they were together

Seán is Jack incase you didn't know by the way.