Melbourne, April 13 : Beyonce Knowles had to work hard and gather her nerves before she performed before legendary blues singer Etta James.

The R&B queen, who plays the 70-year-old veteran in her new movie Cadillac Records, confessed that she could feel the jitters as she sang her idol''s classic, At Last.

"You can only imagine how scary it is when you''re singing someone''s song dressed up as them,'''' the Daily Telegraph quoted her as saying.

"I knew she was very tough and my heart was racing. She had her arms folded and I was like, `Oh, my God! Don''t mess this up, don''t mess this up!''

"Then I did her famous growl and she perked up and looked at her son and punched him on the shoulder like, `That girl is doing it!'' and I was like, `Yes, I got her!''

"At the end I hugged her and wanted to cry, because she''s one of my heroes. She is definitely happy with the movie,'''' she added. (ANI)