'Doctor Who' star Matt Smith and Daisy Lowe have split.

The 29-year-old actor and the 22-year-old model - who have been together for 18 months - are thought to have come to the decision as their respective work commitments made it tough for them to spend a lot of time together.

A friend of the pair told The Sun newspaper: "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.

"They always seemed so happy together. Matt was besotted with Daisy and she adored him."

Matt is also thought to have felt "uncomfortable" about idea of tying the knot with the brunette beauty one day.

The pal added: "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."