Helena Bonham Carter thought 'The Crown' boss Peter Morgan found it ''insulting'' when she didn't agree to take on the role of Princess Margaret right away.

The 54-year-old actress was apprehensive about taking on the part of the late royal at first because she had to follow in the footsteps of Vanessa Kirby, who had already won a BAFTA for her portrayal of Queen Elizabeth II's sister in the award-winning Netflix series.

What's more, the 'Ocean's 8' star wanted to have some time with the script before she decided if she was able to do the job.

Helena admitted: ''With Margaret, I was very conscious that I was inheriting a hit. I was conscious that Vanessa [Kirby] had just won a BAFTA.

''At the beginning, the first two weeks, everyone was terrified. Then you relax.

''But the other thing was I have to see a script and have to respond to the words. People were shocked that I wouldn't just take it.

''I think [creator Peter] Morgan thought I was insulting them, and I wasn't. I just needed to know whether I could do it.''

The 'Fight Club' star - who appears as Margaret in seasons three and four - admitted she had a ''lack of faith'' in herself about whether she could do the part justice.

On what made her say yes, she said: ''He sent me the last episode, which is a really good Margaret episode, and I knew instantly, 'Yeah, I know how to do this.'

''That was why I took so long -- it wasn't a lack of faith in them, it was faith in myself.''

The British actress also admitted that her ''insecurity and anxiety'' made her go to ''ridiculous lengths'' to nail the role.

Helena added to The Hollywood Reporter: ''It's insane the lengths to which I go, and it comes from insecurity and anxiety. And also, I enjoy that bit.

''For me, the best part of the job is when I get the part and there are all of these possibilities.

''And if you're playing somebody who's well known, you get to meet all these people and then have these conversations with them. So, yeah, I went to ridiculous lengths.''