The two actors portrayed brothers on the show until Charlie was fired in 2011 following his erratic public behaviour, including repeatedly slamming creator Chuck Lorre, but Jon still looks back on their time working together with fondness.
Speaking on PeopleTV's 'Couch Surfing', John said: ''Charlie and I just hit it off. We had a great first few years on that show.
''It was incredibly smooth, we had a lovely time, it was working really well.''
Discussing when Charlie's wild antics hit the headlines, he added: ''It became one of the first internet s**tstorms, plus there's the fact that all of our jobs are tied into this guy, and we're all his friends...
''It was very, very strange and [there were] aspects of it that I absolutely hated, but you know, I'm thankful for the years that were great.''
Jon recalled how Charlie was sober when the show premiered in 2003 but he believes his 54-year-old friend's split from then-wife Denise Richards in 2006 led to a relapse, ultimately triggering problems on set.
He reflected: ''At first he could handle it, and he was still incredibly professional -- and still lovely, by the way, to everybody on set -- but you could just see that stuff was wearing on him.''
'Platoon' star Charlie previously admitted he struggles to even recognise that person from his wild period and says that during his lowest moments it felt like there was ''some alien or demonic possession going on'' controlling his actions.
He said: ''It feels awful. I can't sit here and lie to you. Some of it is very surreal to this day I don't know how I created so much chaos and ended up in that head space it's as though there was some alien or demonic possession going on.''
When asked whether it felt like himself, he said: ''Not at all - not how I'm existing and feeling today I wish I could make a lot of it go away but they wouldn't call it the past of it wasn't.''
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