The duo frequently collaborated on hit records, including Amy's 2006 album 'Back to Black', and Mark admits to learning a great deal from spending so much time in her company.
The 39-year-old producer explained: ''I think certain kinds of lessons - whether they were studio lessons or life lessons, I learnt [from her]... she was extraordinarily smart and honest and all these things, and definitely had a lot of character things I looked up to. We were good friends.
''There were things I took away from our friendship and looked up to even though I was older, together in a superficial way. So yeah, just those things I think about - [it] could be a period where I think about it every day or it could be a period where it goes away for a little bit - but she's always around in the studio.''
Mark is immensely proud of their success, but admits it may have contributed to Amy's personal troubles and, ultimately, her death in July 2011, aged 27.
He told BBC Radio 5 Live: ''It's kind of amazing. I met this girl and in the course of 10 days, we made this record that we were really into.
''At the same time all this stuff that came with it, [it] might have contributed to her not being here, I don't really know, but they're two different things in my head.''
American Thighs was released on this day in 1994.