The 30-year-old model - who has split from rugby star Danny Cipriani after almost two years of dating - was seen "whispering and giggling" with the 'Glee' actor at a London restaurant at the weekend.
A fellow diner at eatery The Wolseley told The Sun newspaper: "Matthew kept whispering in Kelly's ear and she was giggling like a schoolgirl. They looked extremely friendly - like they were on a date.
"Kelly looked absolutely gorgeous in an elegant dress. You could see Matthew was proud to be with her.
"Danny must be mad if he isn't fighting to save the relationship."
Kelly's agent claimed the pair- who met in Los Angeles - are just friends.
The brunette beauty and Danny, 22, are believed to have split earlier this month following a series of rows.
A source said: "On two or three occasions Kelly has said, 'That's it, it's over' - only for them to sort things out and be back together again the following day.
"This time, though, it looks more serious. It had been Rocky for a while but it's really deteriorated recently."
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