Australian Twins Who Share Same BF to Star in New TLC Sister Series

TLC's got a new reality TV monster in its midst -- a show about sisters who are too close for comfort, including a pair of Australian twins who share the same man ... literally.

The show's called 'Extreme Sisters' -- a new series documenting the lives of 5 sets of sisters from all over the world, but most of them are from here in the U.S. ... with the only 2 foreigners being 35-year-old identical twins Anna and Lucy DeCinque from Perth.

The DeCinque sisters have one boyfriend whom they split between the two of them -- a 40-year-old mechanic named Ben Byrne. They've all been dating each other since 2012.

The sisters from down under are particularly unique -- as they appear to be in the only polygamous relationship out of the 5 sets ... and as tied to the hip as they all seem to be, Anna and Lucy are almost like one person. At least, that's how they present themselves.

They dress the same, finish and repeat each other's sentences ... and as far as their shared BF, they say they're also planning to get impregnated at the exact same time -- while eventually hoping to get married as a throuple as well one day.