River song, steven moffet clarified in an interview was cause of confusion. He basically said she "knows more than one doctor" and she is a recurring captain jack like on and off companion who obviously becomes the Doc's future wife (something moff even gave a strong "implied confirmation" when asked about if that is what was the one reason she would know the Doctor's name).
She from what i read somewhere, is introduced in the 3rd episode when the weeping angels knock her from the future to 21st century earth like what happened to sally sparrow's friend in "Blink".
Btw side note- a lot of fans have had issues with the idea the Doc will settle down w a companion..but steven also stated a while back and this is a paraphrase from his actual words since i don't have the source info handy to cite- " I always beieved the idea the Doctor would not marry if absolutely ridiculous-of course he would-he lives for centuries and would get lonely, he has probably been married many times as he outlives most companions and aaa "lifetime" with a family would pass rather fast from his perspective" he stated at one time he and RTD played w the idea of opening up season a season with the doc having jumped from 900 to 1,000 yrs old after he had settled down w someone and had a new family, wife dies, he steps back into the tardis to resume his lone travels.