World famous physicist Stephen Hawking performs Big Bang Theory theme song in surprise Comic-Con appearance

He's the one man on the planet who science geek Sheldon Cooper is really impressed by. Renowned theoretical physicist Stephen Hawking made a surprise appearance at Friday's Big Bang Theory panel at Comic-Con in San Diego, California. And the 71-year-old genius - who is idolized by Jim Parson's character on the hit show - even apologized to the gob-smacked audience that he could not be there in person during his pre-recorded video segment. Scroll down to see video

Amazing: World famous physicist Stephen Hawking made an pre-recorded appearance before a Big Bang Theory panel at Comic-Con on Friday

Hawking - who has made cameo appearance on the show playing himself - started his message by saying: 'Sorry, I couldn't be there. I got a flat tire - that was a joke. Ha ha!' And the amazing Oxford born physicist and cosmologist joked that he enjoyed playing games with Sheldon. 'When I'm not playing Words With Friends with Sheldon, I like to think about the universe,' he revealed. My hero! Jim Parson's Sheldon gets to meet Stephen on the Big Bang Theory back in April Then, much to the delight of the assembled fans, Hawking decided to explain the Big Bang theory in 17 words by singing the show's theme song. Fans of the CBS show were also treated to impromptu appearances two of the show's actors Melissa Rauch (Bernadette Rostenkowski) and Johnny Galecki (Leonard Hofstadter) at Comic-Con. Rauch moderated the writer's panel while Galecki posed as a fan waiting in line to ask a question dressed up in a Princess Leia bounty hunter disguise from Return of the Jedi. 'I just couldn't stay away,' he told the crowd after revealing himself.

Fan appeal: Johnny Galecki and Melissa Rauch met fans at Comic-Con

In costume: The Big Bang Theory's Johnny Galecki dressed as a bounty hunter from Return of the Jedi to surprise fans at Comic-Con

Surprise! Johnny's costume as a bounty hunter from Return of the Jedi was a big hit

And a day after the show was nominated for the Outstanding Comedy Series Emmy co-creator Bill Prady and show-runner Steve Molaro also dished out some secrets on what fans can expect from season seven of the Big Bang Theory. Fans can enjoy seeing more of the strange dynamic developing between Sheldon (Jim Parsons) and Amy (Mayim Bialik) When asked if they will finally consummate their relationship, Molaro revealed: 'It's a possibility - Amy will continue trying to get her way.' Fans will also see Amy and Bernadette (Rauch) go on a trip together and will see Leonard on the research ship with Hawking when the series returns on September 26.

I'm here! : Johnny gave The Big Bang Theory Panel a shock by appearing in costume

Geek squad: Cast from Big Bang Theory appear at People's Choice Awards in Los Angeles back in January