Adam Johnson engaged in lengthy conversations with a teenage girl using the WhatsApp system, believing she was deleting their messages, prosecutors said.
Kate Blackwell, prosecuting, told Johnson's trial how the exchanges - described by the footballer as "cyber-flirting" - showed he was fully aware the girl was only 15 and still at school.
Miss Blackwell said that when they first started talking to each other she was not convinced he was the real Adam Johnson and he proved who he was by posting a message on his Twitter account.
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He then said to her: "You in the last year at school?"
The prosecutor told the jury how the girl chatted with the footballer about how people said she looked older than her age as they arranged to meet so he could sign a Sunderland shirt.
After the pair met for the first time they again took to WhatsApp to discuss the meeting and whether Johnson should have a "thank you kiss" for signing the shirts.
In one exchange, according to Miss Blackwell, the girl said: "Why didn't you ask yesterday for a thank you kiss?"
The defendant replied: "I just didn't think you would want to."
The girl said: "Wouldn't have bothered me."
In a later exchange, Johnson asked the girl: "Am I only getting a kiss?"
She replied: "Depends what else you're after."
He said: "Dunno ... depends what you're up for."
And he added: "A bit more than kissing."
Miss Blackwell told the jury that Johnson told her to delete their conversations, at one point telling her: "Don't forget to delete this convo please."
The girl eventually convinced the footballer to move their conversations on to Snapchat, where no record is left.
Miss Blackwell told the jury the exchanges were "messages that he had deleted, that he had requested be deleted by (the girl) and that he believed her to have deleted."