According to New York Daily News, the identity of the woman is physiotherapist Heather Milligan, who runs a practice in Westchester, California and regularly treats NFL players.
While the press have tried to coax a comment out of Heather, so far the only comment she's made was a tweet back in July, which she since deleted on Tuesday.
"Happy Birthday to @Schwarzenegger!!" she tweeted. "Headed to the gym to shock the system and get more than one percent in ... Thanks for inspiring so many."
It's not clear yet whether Arnie and Heather are a serious item, but judging by his smirk in the photos and video above, it looks like he's having fun.
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