Jennifer Aniston, Justin Theroux cheating rumors? Wedding on hold, actor 'flirts' with mystery blonde at party amidst pregnant/baby bump buzz

Rumors continue to rapidly swirl online that Jennifer Aniston is pregnant with fiance Justin Theroux's baby. As Mstars previously reported:

Jennifer Aniston 'pregnant and alone,' Justin Theroux ditches wedding plans and storms off to work in NYC?

Jennifer Aniston pregnant with twins? Baby bump, fertility treatment rumors hit Justin Theroux's fiancee AGAIN, couple hiring nannies for future sons?

Jennifer Aniston Pregnant RUMORS: Justin Theroux's Fiance Baby Bump Buzz amid Wedding Plans, 'Scared' of Miscarriage, Drinks 'Only Water'

Jennifer Aniston 'Pregnant and Alone,' Justin Theroux Wedding Off? 'Fighting' Leads to 'Toxic' Relationship, Starlet's 'Worst Nightmare Comes True'

The 44-year-old actress continues to deny such baby bump talk, insisting that if she were indeed expecting, fans would here the news from her first.

Well, NOW the seedy gossip tabloid Star claims that Theroux might be cheating on the former "Friends" starlet... and their relationship (and marriage) is in jeopardy.

According to the magazine, the "Wanderlust" actor attended Robert Downey, Jr.’s birthday party for his wife Susan last weekend. Aniston wasn't there. In fact, the couple hasn't been spotted together for awhile. Of course this gives Theroux a reason to let his eyes stray...

One alleged insider reveals, "Because it was a family event, people were stunned to see that Jennifer didn't attend with Justin." Star continues,  "Eyebrows were raised even further when Justin was spotted getting affectionate with an attractive blonde, even sharing an embrace with the mystery woman."

The insider explains, "He gave her a friendly kiss and a hug when she walked up, which is normal. But what was abnormal was the fact that they were touchy-feely and stood around with their arms around each other... Justin's close affection with the blonde was definitely the talk of the party."

FYI - it turns out this "flirtatious" mystery woman was actually Trudie Styler, the wife of Sting! Theroux and the singer have been friends for years.

Wrong again, Star.

Theroux's allowed to hug a friend that's a woman - it doesn't mean he's cheating on Aniston. In fact, their relationship seems to be going just fine. Maybe Star should find an eyewitness who's better with identifying famous people.

Anyway, a source close to the situation tells Gossip Cop, "They were saying goodbye upon leaving the party." This source insists that such cheating rumors are totally "ridiculous."

The couple's wedding is NOT on hold - they're just taking their time planning it.