Sad but true: Mark Harmon has left NCIS after 18 years. Since 2003, the actor had been in front of the camera as Special Agent "Leroy Jethro Gibbs," becoming a true TV legend. But now, in season 19, it's over. Here's how fans are feeling about the news.

Mark Harmon exits: NCIS fans are sad

For quite a while, there were rumours about how things might end with "Gibbs" on NCIS. Fans hoped for a happy ending — and many were bitterly disappointed.

"I'm not going back, Tim ... I'm not going back home," the NCIS boss said to "McGee" — a heartbreaker for all fans. Responses to the exit of the former "Sexiest Man Alive" Mark Harmon have been enormous.

"I don't usually mourn TV characters, but when I saw #NCIS say goodbye to 'Gibbs' / Mark Harmon after 19 seasons, it broke my heart," writes a fan on Twitter.

Another user says: Even thought we knew this was happening, it feels surreal and I still don’t think #NCIS will be the same. Others can come and go but Mark Harmon/Gibbs IS the foundation of NCIS." Many thank the actor: "Thanks for the 18 years, Mark."

NCIS fans declare: No "Gibbs," no show

Some fans, on the other hand, reach drastic conclusions and write: "That should just about do it for the original NCIS! No Gibbs No NCIS." 

One user thinks that the sad NCIS exit by Mark Harmon could mean the end of the series: "This is probably the last season for NCIS because Mark Harmon (Gibbs) was the main attraction."

A quieter crowd, however, felt that Harmon was somewhat checked out in recent seasons, and it was time for "Gibbs" to move on. Many suspect Gary Cole's "Alden Parker" will now become the boss at NCIS.

But the frustration of NCIS fans is great. After all, Harmon was one of the original stars of the series. But it may not be goodbye forever.

If showrunner Steven Binder has his way, future guest appearances aren't ruled out: "Regarding the future of Gibbs, as long-time fans of the show may have noticed over the years… never count Leroy Jethro Gibbs out."

Perhaps this statement is a small consolation for fans. Season 19 resumes with Episode 5 next Monday, Oct. 18.