Dame Helen Mirren is to provide the "inner voice" of a character on Glee. The Oscar-winning actress has recorded lines for an episode of the musical TV show - starring Matthew Morrison, Lea Michele and Heather Morris - where she will be heard but not seen, although the part whose inner thoughts she will be voicing is not known, according to The Wrap.

The episode, titled "Yes/No," will feature Matthew's character Mr. Schuester and Jayma May's Emma prominently. "Helen recorded several long, hilarious monologues recently. She visited the kids on set - they had no idea she was coming and were stunned," a source said.

Glee is renowned for attracting big name stars onto the show, including Gwyneth Paltrow - who played substitute teacher Holly Holliday - and Britney Spears, who appeared as herself. However, Britney's appearance was not easy for the regular cast members of the show as they had to have special security on the day. "What was Britney like? I don't know - I didn't get to meet her. Not many people did. She had pretty big security around her. We actually had security bands to get onto our set that day," Matthew said.