Former Doctor Who star David Tennant has issued an enigmatic warning to new companion Jenna-Louise Coleman: "Keep your nose clean, watch your back!" 

"She'll have a brilliant time, I'm very jealous of her starting out on that extraordinary journey," said Tennant, "but, you know, keep your nose clean, watch your back!

"You're suddenly rocketed into a world of attention, certainly unlike anything I'd known before," he told Digital Spy. "You just need to watch your back a little bit... But it's wonderful. It's such an exciting thing to be starting out on."

It's not the first time Tennant has hinted at the stresses and strains of working on Doctor Who. Last week, following Coleman's unveiling, he said: “I hope she has some good friends to hold her hand because it can be a bit scary when you get thrust into that level of attention, speaking from personal experience."