Mavor, who will play Mini in the new series, explained that she was already a fan of Addison because of In The Loop and The Thick Of It.
"He was amazing," she said. "He was just the biggest joy to act with... He was just such a joker. I loved him so much. He was great - he was like one of us. It was just like chilling with a friend."
Mavor also revealed that Addison had helped her with becoming an actress, saying: "He gave me such good advice. I had scenes where it was just me and him sometimes and he had really good advice to give me. At the same time, he was so funny and he just had so much energy. He was an absolute joy."
The fifth series of Skins begins on January 27 at 10pm on E4.