Katy Perry is reportedly "mad about" Robert Pattinson, but is scared of getting hurt again.

The Dark Horse singer and 28-year-old actor have maintained a close friendship over the years and both have dated other people during the time. Rob previously had a relationship with his Twilight co-star Kristen Stewart, while Katy was married to Russell Brand and has dated the likes of John Mayer and Rob Ackroyd.

It is thought the pals have feelings for each other, but Katy fears the relationship could fail just like with her former other halves.

"She's mad about Rob but is so terrified of getting serious and hurt again," a source told British magazine Look. "I think that's why she's trying not to get too involved romantically. She'll also be super cautious of becoming one half of a celebrity couple yet again.

"Rob's behaviour makes it clear to anyone who sees him with Katy that he's interested in taking their friendship further."

The pair have been spotted out frequently since their friendship began, most recently at the premiere party of Rob's film The Rover. They were said to have been "hugging and kissing" the entire evening.

"The chemistry is undeniable. Rob can be surrounded by women but seems only to have eyes for Katy. They're very close," the insider added. "From the sound of it they talk every single day, by phone, by Skype, by text."

Amid these reports, Katy is also said to still be close to DJ-and-producer Diplo. Earlier this month it appeared they were both on holiday together after they posted photos on social media which seemed to confirm they were in the same location.