Karna was known all along

 We are told that karna was abandoned by kunti. in the ganges in kunti rajya and he floated and reached Hastinapura kingdom (or anga accordig to some versons) and Adiratha found him and brought him home and adopted him.Then later Kunti chooses pandu in swayamvara,and reaches hastinapura.This is not a coincidence.Kunti found out where karna reached and who has adopted him.She inquired about a boy found on the ganges,and found out that Adiratha a suta,a charioteer and a minitser of Dhritarashtra has adopted him.When a swayamvara was arranged she deliberately chose pandu,the king of hastinapura.So that she can stay in hastinapura where karna is brought up.After she went to hastinapura she met karna as a child.karna is four years older than yudhishtira.Pandu was impotent so she had children by niyoga through other men.She was constantly watching karna as he grew up.She talked to him till he reached adult age.He knew her as queen as hastinapur and also as former queen.But didnt know she is her mother.Kunti knew karna is her son.
The kmg version says when karna entered then rang bhoomi,and challenged Arjuna kunti recoginised him with many auspicious marks on him.This is not true.She already knew that he is her son,She could have even provided Adiratha financial help for karna.But she didnt admit that karna is her son even when karna is called as a suta putra,and denied admission to Drona's gurukul or denied from contesting with Arjuna as he is not a prince.That was her mistake.She told karna that he was her son just before the mahabharata war.Bu that time karna was a friend of duryodhana for a long time,and could not abandon him.But he said he will spare four pandavas other than Arjuna.She was talking to him throughout the mahabharata.This was well shown by star plus mahabharata.They were right in showing the kunti karna relationship.Kunti going to karna just before the war and asking for boon is false.Why will karna grant any boon to someone who abandoned him after he was born.karna was known all along to kunti.If she said he is her son at the time of raja suya yaga,he would have come to the pandavas side.