The 33-year-old actor – who replaced troubled star Charlie Sheen on the CBS sitcom after he was fired following a public spat with the show's creator Chuck Lorre – first appeared on set last Monday, but the atmosphere was so strained onlookers could "cut the air with a knife".
Nina Tassler, CBS programming chief, explained: "When everybody walked on the set you could cut the air with a knife."
However, the tension was quickly broken by 'Two and a Half Men' star Jon Cryer – who portrays Charlie's on-screen brother Alan Harper – who delivered a "touching" speech to the cast and crew.
Nina added to Fox News: "He gave a little speech. I can't even remember the words. It was just something very touching.
"Then, when you hear that first actor mutter that first line, you breathe a sigh of relief."
Ashton is to play Walden Schmidt, an internet billionaire with a broken heart, and show bosses promise 'Two and a Half Men' will be "as irreverent" as when Charlie was the main star.
Nina said: "The show will be as irreverent as it has ever been."
Ashton recently compared landing the coveted role to "winning the lottery".
He explained: "I've never probably in my 13 years in show business received more phone calls and emails from people congratulating me on this job.
"You'd almost think I won the lottery or something, which I kind of did. I've got the best job in showbusiness, and I am ecstatic about that."
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