David Walliams says "regular sex" is the secret to Simon Cowell's new sunnier disposition on 'Britain's Got Talent'.

Simon Cowell

Simon Cowell

The former 'Mr Nasty' is transformed on the upcoming season of the reality TV show, with co-judge David Walliams claiming that Simon's girlfriend Lauren Silverman should get full credit.

Speaking at a press conference for the latest series, David quipped: "He's been in a very good mood this year... He's having regular sex."

Simon, 56, has been dating Lauren, 38, since 2013 and the couple have a two-year-old son, Eric, together.

However, David joked that he and Simon have a great deal of "sexual tension" between them, explaining: "[The sexual tension] will be released at some point. It's 10 years of the show and I think in the final episode, that's what we'll do.

"We're like brothers. But brothers who like to cuddle."

David, 44, also poked fun at Simon's friendship with former 'X Factor' judge Louis Walsh, claiming they share a bed.

He teased: "If I was Simon I'd get up at 4pm in the afternoon. 'Louis, it's time to get up'.

"Roll into work at 8pm. Judge for 10 minutes then stay up all night doing something really really awful."