The model and Doctor Who star have reportedly called time on their 18-month-long relationship.
A source told The Sun that it was work commitments and Matt's reluctance to settle down that led to the split:
"Whenever engagement and marriage was mentioned he was uncomfortable. He's still a young man and the thought of being tied down was a lot to digest.
"This has come as a surprise to everyone. It was thought they'd be together for a really long time because they were so into each other."
The pair reportedly got together in April 2010, before splitting in May. They then rekindled their romance in July of the same year.
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