Isla Fisher is completely unrecognisable after debuting her new blonde tresses.

The 42-year-old 'Confessions of a Shopaholic' actress has ditched her signature red locks and opted for a golden blonde look which she unveiled to fans via a snap on social media on Tuesday night (01.01.19).

Speaking to her one million followers on Instagram, Isla captioned the picture: ''Go blonde in '19 or go home''.

The Australian star has reportedly been cast alongside Steve Coogan and David Mitchell in filming the Michael Winterbottom-directed movie 'Greed'.

In the upcoming film, Coogan will play the part of a self-absorbed retail billionaire, according to Deadline, which reports that Isla will appear as his on-screen wife.

Isla's character is said to be the only person who can truly understand the businessman and his complex personality.

Winterbottom is helming the movie on behalf of Film 4 and Sony International.

But before 'Greed' is released in cinemas, Isla will next be appearing in the upcoming comedy flick 'The Beach Bum', which also stars the likes of Zac Efron, Jonah Hill and Matthew McConaughey.

Meanwhile, Isla - who is married to British comedy star Sacha Baron Cohen - recently admitted she respects her husband even more since they worked together.

The actress - who has kids Olive, 10, Elula, eight, and Montgomery, three, with Sacha - shared the screen with her husband in 2016's 'Grimsby' and she subsequently admitted there's no one she'd rather make a movie with.

She said: ''We had a really fun time [on 'Grimsby']. We shared a trailer. And it was just hilarious.

''Obviously I always respected him, but having been around so many big comedy stars and seeing how they improvise and stuff - and then to work with my husband and see him be the best improv comedian I've ever worked with, I loved it.''