Gillian Anderson is in talks to join the cast of 'The Crown'.

The 'X Files' actress' partner, the show's screenwriter Peter Morgan, is reportedly keen to get the 50-year-old actress on board as the late British Prime Minister Lady Margaret Thatcher, who is expected to appear towards the end of the fourth series when she was elected as leader of the Conservative Party.

A source told the Daily Mail newspaper: ''Gillian is an excellent actress, so it would be a real coup to get her.''

Gillian and Peter - who have been together since 2016 - declined to comment on the reports, but the 55-year-old writer has previously said he'd like to work with the 'Fall' star again.

He said last year: ''We worked together on 'The Last King Of Scotland'. We were both married and that was a lifetime ago. I would work with her again.''

Filming is currently underway on the third season of the regal Netflix drama, which sees Olivia Colman and Tobias Menzies take over from Claire Foy and Matt Smith as Queen Elizabeth and her husband Prince Philip, roles which they will also keep throughout season four.

Meanwhile, Helena Bonham Carter - who is taking over as Princess Margaret from Vanessa Kirby - recently admitted she and her co-stars were ''terrified'' about working on the show and having to make their parts their own.

Speaking before filming began, she admitted: ''I've definitely started prepping. It's exciting.

''We start in a few weeks, and I think we're all -- we're completely terrified.

''I think also because the first two seasons were such a success, we have the onus of inheriting the responsibility of doing justice to all these genuinely famous people, and then on top of it, inheriting them from this previous generation of actors who've done such good jobs.''