Jeffrey Dean Morgan has defended himself for wearing a Blue Lives Matter T-shirt.
The Walking Dead star says he backs the controversial cause, which was set up by US police officers, but also supports Black Lives Matter.
"Can't believe I need to explain to you this fact. All lives matter. All of em," he wrote.
Blue Lives Matter was started after the deaths of two New York police officers in Brooklyn in 2014.
Rafael Ramos and Wenjian Liu were ambushed in their patrol car.
Their killing has been seen as a response to the deaths of Eric Garner and Michael Brown, unarmed black men shot dead by police.
"This shirt was made in response to the cold blooded murder of two GOOD cops in NY, both that had immigrated to the US, and took an oath to protect and serve," Jeffrey wrote on Facebook.
"This shirt was given to me at a convention by a woman, whose son, was shot during what was a routine traffic stop. He was black."
The actor, who plays Negan in The Walking Dead, has been criticised on social media for posting a photo of himself in the shirt.
Blue Lives Matter was started by a group of retired and current police officers, to counter media reports that they felt were anti-police.
Controversially, it has led to a state law in Louisiana making violence against police officers a hate crime.
The 51-year-old originally responded saying his critics should "grow up".
But he has since posted an Instagram statement saying sorry for offending people.
"I stand behind the sentiment... but, what was meant as one thing has been taken as another. I understand those that are upset... and to those people I apologise.
"Of course black lives matter. I stand behind that. Always have.
"This country means the world to me. The good people in it mean the world to me... the ones [sic] looking for a fight around every corner? Racists? Bullies? They don't. We are a country divided and it's getting scarier every day."