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The 42-year-old is known in Hollywood as the "Disso Queen" for her speciality in marriage dissolutions and previous A-list clients have included Angelina Jolie and Mel Gibson's ex-wife Robyn.
A source told People magazine: "Maria hasn’t decided yet whether she wants to end her marriage."
Meanwhile the housekeeper with whom Arnold fathered the child over a decade ago has been revealed as Guatemala-born Mildred Baena.
The 50-year-old staff member - who worked for the Schwarzenegger family for 20 years - separated from her husband Rogelio de Jesus Baena just days after giving birth to her son.
When the couple filed for divorce in 2008 Mildred did not list Rogelio as the baby's father. This, however, contradicts a birth certificate obtained by People that identifies him as the father.
The boy - who has not been named - was born less than a week after Maria and Arnold's youngest son Christopher.
Neighbours of the mother and son - who live in a quiet town north of LA - have described the 13-year-old as a polite and athletic youngster, who was involved in charity.
One neighbour said: "When he came over selling his fundraising stuff he told my husband his mom worked for Arnold Schwarzenegger."
She added: "But it was not like 'he's my father' or anything like that. I have no idea if he knew that or not."
"The child is very well reared, he does not say 'yes ma'am or sir' but close to that. My husband and I are very sad and worried that this is going to affect this young man."
Sixty-three-year-old Arnold has been providing financially for the boy since learning of his paternity shortly after he was born.
Neither Mildred nor Rogelio have commented since the Terminator star confirmed the revelations.
It's a little princess!