Artem Chigvintsev's domestic violence arrest didn't come out of left field, at least according to people who say they know him and Nikki Bella ... they tell us the relationship has always been "volatile."
Sources with direct knowledge tell TMZ … Artem and Nikki's close friends, including their former 'DWTS' cast and crew members, are not entirely shocked by Artem's claims Nikki threw shoes at him during a heated exchange.
We're told Artem and Nikki's marriage has been troubled for some time, and it wasn't exactly a secret to anyone in their orbit.