It was previously claimed that scriptwriters had been hoping to include Thatcher in an episode covering Queen Elizabeth and Prince Philip’s golden wedding anniversary.
“Gillian’s portrayal of Thatcher was met with global critical acclaim and she was a huge asset to The Crown,” a source told the Sun.
“It had been hoped she would be able to make an appearance in scenes around the golden wedding but sadly that has not been the case due to scheduling issues.
“As ever with the series, clever scripting will mean viewers will be none the wiser.
“But it’s been another blow for producers in what’s already been a fairly dogged production.”
Season six of the Netflix royal drama depicts the events leading up to Diana, Princess of Wales’ 1997 death.
The Crown – one of Netflix’s biggest hits – was initially set to end after five seasons, however, because of demand and the complexity of the storylines a sixth and final series was added.