David Walliams says Simon Cowell's youthful appearance makes him look like he's had a ''terrible accident''.

The 46-year-old comedian has poked fun at his 'Britain's Got Talent' co-star, who previously admitted to being a fan of Botox injections.

David quipped: ''His face has always changed. Something has happened. You think, 'What has gone on? What exactly? Did you have a terrible accident or something?' Yeah, he always looks a bit different.''

David also joked that the music mogul never makes an effort to see him when they're off camera.

He told BBC Radio 2: ''We are friends when the show is being made. He will sort of invite you out for dinner and you think, 'This is great I am having dinner with Simon Cowell'.

''And then you don't hear from him for six months when the show is not on and then he will be back in touch in January.''

Simon, 58 - who has four-year-old son Eric with his long-term partner Lauren Silverman - previously admitted to having had a so-called 21st century facelift.

The procedure - which involved sewing bioplastic-infused thread into Simon's face - is designed to hide sagging skin and generally create a more youthful appearance.

Speaking earlier this year, he explained: ''There's lots of things you can do now. You don't just have to stuff your face with filler and Botox.

''It hurts like hell but it gets rid of sun damage and unplugs all the crap. For me now, it's all about having clean skin. If you have clean skin, you look better. But you have to be very careful with some of this stuff.''

Simon also previously admitted to having had too much Botox.

He shared: ''I probably did have a little too much a couple of years ago.''