Could this Chicago Fire star be joining the cast of NCIS to replace Mark Harmon?

Gary Cole is reportedly being lined up for a season 19 role

NCIS will reportedly welcome a brand new star into the fold of its main cast when it returns later this year for its 19th season - and now fans are fearing for the worst following the continuing rumours that Mark Harmon wants out of the series.

MORE: Where are the stars who left NCIS now?

Although not officially confirmed by CBS, Chicago Fire and Mixed-ish actor Gary Cole is being lined up for a part on the long-running franchise. Details about his character remain under wraps for now, but according to Variety, the actor is set to join the cast in a major role.

Shortly after the news broke, many fans of the show took to Twitter to give their thoughts.

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WATCH: Katrina Law makes her NCIS debut in season 18

One frenzied fan wrote in reply to the news: "Is he going to replace Mark Harmon?!" Another said: "OK, re these rumours about Gary Cole - I just don't see it surviving without Mark Harmon."

MORE: 5 shows to watch if you can't get enough of NCIS

MORE: Major change for NCIS announced ahead of season 19

However, some were more positive. "Gary Cole is a great choice to head the @NCIS_CBS team until Mark Harmon shows up again," one wrote, while someone else added: "Oh my God I am now SO EXCITED after reading that Gary Cole might star in NCIS and have a big role."

According to sources, the actor may not be the only new face joining the show's main cast in the new season and fans should expect to hear more casting news in the coming months.

Many fans are once again concerned about Mark Harmon's future on the series

It's likely that former Hawaii Five-0 star Katrina Law, who was introduced as REACT agent Jessica Knight in the penultimate episode of season 18, will take up a place on the team following Emily Wickersham's character Ellie Bishop's shocking season finale exit.

MORE: Who is Katrina Law and who does she play on NCIS?

This year has seen several major changes to the NCIS franchise. While it was announced in February that NCIS: New Orleans would end with its current season, new series NCIS: Hawai'i will be the first with a woman at the helm - and the first set outside mainland USA.

It's been confirmed that actress and TV presenter Vanessa Lachey will take on the role of Jane Tennant, a female officer who has risen through the ranks to become the first female Special Agent in Charge of NCIS Pearl Harbor. Joining the Love is Blind host in the cast are Yasmine Al-Bustami and Jason Antoon, who will play two junior NCIS agents.

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