|Dame Helen Mirren|
The episode, titled 'Yes/No', will feature Matthew's character Mr. Schuester and Jayma May's Emma prominently.
A source told the Daily Express newspaper: "Helen recorded several long, hilarious monologues recently. She visited the kids on set – they had no idea she was coming and were stunned."
'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.
Matthew said: "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."
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