It was American Idol's newest judge Ellen DeGeneres first day of taping the Hollywood segment, and she was excited and nervous, sources tell us. But then that turned to anger. Because, our insiders say, Simon Cowell was an hour and a half late for the taping. And Ellen stewed while she waited. She had reason: to accommodate both her talk show hosting duties and her American Idol judging duties, she had moved up her schedule so that now she shot the talk show earlier in the day and then jumped in the car to go to Idol. She was on time, and Cowell was not. "Here it was the first day of taping of the Hollywood shows, and Ellen was there waiting for Simon to show up. Ellen's new to gig and she's very organized and she made a commitment to take this on, and now she's asking herself, 'What did I get myself into?' She called Simon Cowell a prima donna. So right from the start, the chemistry isn't great," an insider tells us.