The rapper and Winehouse's duet appears on the late singer's posthumous release Lioness: Hidden Treasures, which compiled recordings meant for her third LP.
"It's a bittersweet feeling to do something with her now that she's not here. I'm happy... the sweet part is that we do have the music, fans have new music from her," Nas explained to World Star Hip Hop.
"It's new because they've never heard it. The bitter part is that she's no longer here to really give it to us and to really live her music and for us to see her smile and hear her voice."
Nas praised Winehouse for her incredible talent as well as her ability to resist the pressures of industry execs, recalling: "The first time I heard Amy, Salaam Remi was producing some stuff for me, we were working together again and he played me her stuff. I was like... instantly, the voice just caught me and that was in, like, 2004.
"She was hilarious, man. She would make you laugh. To her, music came so easy. To everyone else, I guess around her, I don't know this but I'm assuming that they wanted her to put out a new record.
"To her, it's like, she can't do it until it's really time. Whatever that time is, only time will tell. She can't just give you a record because the fans want it, she's hot or it's going to sell records. That's not her style. She was so nonchalant about it that it reminded me of myself."
Lioness: Hidden Treasures has raised hundreds of thousands of pounds for the Amy Winehouse Foundation since it debuted at number one on the UK album chart earlier this month.
Listen to Amy Winehouse and Nas on 'Like Smoke' below: