Outlander’s Caitriona Balfe struggled with an iconic line from the original novel series.

The Starz time travel drama may have found a global audience when it hit the small screen but there was a large fanbase long before its existence thanks to the books.

Author Diana Gabaldon published her very first Outlander novel way back in 1991 and is now in the middle of writing the 10th in the saga.

It wasn’t until 2014 that Starz released the first series which, much like the following seasons, sticks to the plot and characters in the books for the most part.

However, this isn’t always easy as Claire Fraser star Caitriona Balfe quickly discovered.

Outlander’s Tobias Menzies reveals Caitriona Balfe’s struggle over iconic book line. (Image: STARZ)

Fans of the book series are very familiar with Claire’s catchphrase “Jesus H Roosevelt Christ”, a term she originally learned from an American soldier.

She frequently used the phrase whenever she got frustrated, particularly in the early seasons, much to Starz subscribers’ delight.

But opening up to Backstage, ‘Black’ Jack Randall star Tobias Menzies said how his co-star had questioned the use of this important line.

He said: “There were some quite overt direct speeches in the novel, which can be quite bumpy.”

Outlander: Claire Fraser star Caitriona Balfe has struggled with the phrase ‘Jesus H Roosevelt Christ’. (Image: STARZ)

“An example is Claire’s ‘Jesus H. Roosevelt Christ.’

“Which obviously all the fans are obsessed with.

“But I know Cat spent a lot of time going: ‘I don’t know how to make this work for me.’

“She really wrestled with it. And that’s part of the adaptation process.”

Outlander’s Black Jack and Claire Fraser played by Tobias Menzies and Caitriona Balfe. (Image: STARZ)

Thankfully, the show chose to stick with this crucial line, despite Balfe’s difficulty with saying it.

Although there have been times when the cast have had influence over the script.

Sam Heughan spoke of an open-door policy with the writers, describing them as “really fruitful”.

He continued: “You are the one person who is looking only at that journey, that one character.

“The writers are looking at the structure and different characters and how they all kind of interact.

“So it’s always an interesting thing to stand up for.”