Ben Affleck's girlfriend Jennifer Garner has sparked reports she's pregnant with the "Pearl Harbour" actor's baby after she was photographed with a bulging stomach.

The couple had met on the sets of 2003 movie "Daredevil" and reportedly got engaged 11 days ago fuelling rumours they are expecting a child, reports Internet Media Database.

Celebrity experts insist it's unlikely Garner's swollen belly is a result of over-eating or lack of exercise because she famously devotes herself to a gruelling health and fitness regime.

"Jennifer was showing quite a big bump and she was walking very carefully. The bulge is out of proportion with the rest of her body, which is really toned. I'd say she's a few months gone," an insider was quoted as saying.