The pair will appear together in a forthcoming Sarah Jane episode, which will also see the return of classic Doctor Who companion Jo Grant (Katy Manning).
"There's a lovely moment when Sarah realises just who Jo is," Sladen told Total TV Guide. "And as for Matt Smith, he is a bloody alien, isn't he? He doesn't have to act! I can see exactly why they cast him. He was a joy to work with. He went for it on every take."
The actress also described the opening two-part adventure of Sarah Jane's fourth series, titled 'The Nightmare Man', as "scary".
"The Nightmare Man gets into your mind and plays nasty tricks," she explained. "I got to play an evil version of Sarah Jane, who appears in Clyde's nightmare. I relish those moments when the writing allows me to be something other than Sarah Jane, kicking ass."
The Sarah Jane Adventures returns to the CBBC Channel on October 11.