Speaking to ThisIsNottingham, Marcus praised Gary for being "a man of his word" after promising on the show to help him with his singing career after the competition ended.
"It was pretty odd the first time he came round for tea," he told the website. "Gary kept quizzing all my family, trying to get the gossip, but there isn't really any.
"Then him and my nan sat talking for hours. They could talk a glass eye to sleep, them two."
Marcus, who finished second on last year's series to Little Mix, went on: "Gary's a man of his word, though, and when he says he wants to help me with my career, he means it.
"You only have to look at all the charity work he's done to see that he'll go the extra mile to help people."
The Liverpudlian singer added: "I can learn a lot from him."