The 28-year-old 'Read All About It' rapper was a guest on Nick Grimshaw's Radio 1 breakfast show when he took part in Call or Delete, a game where celebrities either prank-call or erase someone in their phonebook.
Calling the Made in Chelsea star live on air this morning (October 10), Green said: "You know how I'm a big fan of Grimmy? Well, he was just really odd this morning. Since he's started doing the breakfast show… it was like meeting a different person.
"He was really up himself and was rude about us. He was saying we were just a celebrity relationship."
Green, real name Stephen Manderson, continued with the prank, adding: "But then something else happened. As I was coming out I bumped into Imogen Thomas."
22-year-old Mackintosh replied: "Why would you even talk to her? You got papped talking to her?"
Green then told her: "There's a coffee shop right on the corner of Radio 1", to which she said: "You got papped having coffee with Imogen Thomas? Oh my God. I can imagine the headlines already."
The rapper quickly added: "I'm so sorry. We were definitely not holding hands. It wasn't anything like that, it was completely innocent."
Grimshaw phoned Mackintosh afterwards to explain, telling her "I feel so bad".
After the incident, Mackintosh joked on Twitter: "Let's just say someone isn't getting any.... For a while."
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