Cesar Millan is being investigated for animal cruelty following an incident on the former "Dog Whisperer" star's current reality show.

The complaint was made against Milan's Dog Psychology Center, north of Los Angeles, on Thursday.

The complaint possibly stems from an incident in which a dog fearful of pigs attacked a pig during a training session on a recently aired episode of his current show, "Cesar 911" on Nat Geo Wild Channel.

"There was a complaint that we received and we are investigating the matter," Deputy Director Danny Ubario of L.A. County Animal Control, told TheWrap.

"An officer visited the center today and it is currently under investigation."

When investigators arrived at the facility, family members said Millan was away on a business trip.

Millan must comply to a 24-hour notice from animal control about the well-being of the pig.

The incident on the show outraged some animal activists and other dog trainers, inspiring professional dog trainer Laura Nativo to organize a petition demanding the cancellation of Millan's Nat Geo Wild Channel show.

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Nearly 8,000 signatures have been collected so far.

"It was really difficult to watch," Nativo said. "It's not the way to rehabilitate an animal that is fearful and and aggressive to pigs."

Millan is a self-taught dog trainer. His previous show, "Dog Whisperer with Cesar Millan," aired on the National Geographic Channel and its Nat Geo Wild sister network from 2004 to 2012.