Viewers were quick to call out Luke Bryan for appearing to check his left hand at moments during his performance of the National Anthem at the MLB All-Star Game in Kansas City, Mo. on Tuesday night. Now, the singer has come clean, admitting to have written "key words" down to ensure he did his best.

In a series of tweets on Wednesday morning, the 'Drunk on You' singer explained why he did it. "I had a few keys words written down to insure [sic] myself that I wouldn't mess up. I just wanted to do my best. I promise it was from the heart," he wrote.

"If I offended anyone with my approach I sincerely apologize," he added. "Anytime I sing the anthem it is an honor and my heart beats out of my chest."

Bryan's anxiety is certainly understandable, as singing in front of a nationally-televised audience is amongst the most nerve-wracking things an artist can do -- and typically fans are unforgiving when you mess up. However, few questioned the quality of the Georgia native's performance.

"I did check my watch because I knew the stealth bomber would fly over 2 minutes in and I knew a started a little late," Bryan said in response to another theory as to why he looked down at his arm. The plane's entrance was timed perfectly.

To wrap things up, Bryan seemed hopefully about future star-spangled performances. "Being a part of the all star game was amazing and I look forward to the next time I can perform the anthem." he said. "Thanks y'all. Love ya."

Watch Luke Bryan Sing the National Anthem at the All-Star Game

More From Taste of Country