EXCLUSIVE: Chris O'Donnell on Why You Don't Mess With LL Cool J: 'He is a Force to Be Reckoned With'

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Season eight of NCIS: Los Angeles premieres on Sunday, and ET stopped by the set, where star Chris O'Donnell compared it to a family reunion.

"The cast especially can, a lot of times, feel like your siblings," O'Donnell says. "There are days that you love each other and days that you hate each other."

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Siblings are known to have the occasional scuffle, but no matter how much co-star LL Cool J (real name: James Todd Smith) feels like O'Donnell's brother, the two won't be going to toe to toe.

"That dude is one of the strongest dudes you can ever run into, as we all know," O'Donnell points out. "Todd is a force to be reckoned with."

But is that force strong enough to get O'Donnell to perform on LL's other show, Lip Sync Battle?

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"I hope to get some of the guys from this show over there at some point," LL tells ET. "That would be a lot of fun."

NCIS: Los Angeles returns to CBS on Sunday at 8:30 p.m. ET/PT.