Rescuers moved 14-year-old Murlitharan from a hospital to a shelter in the Andamanese capital of Port Blair and told him that his 12-year-old sister, who had also been reported lost, had been traced.
And he also spoke by telephone with his father, Radha Kishan, in the Indian city of Madras where he had taken his injured wife after listing his two children as lost under the tsunamis that ravaged Nicobar island.
"In fact, I had seen actually my sister on my second day on the tree but my throat was so parched that I could not call her," said Murlitharan, whose first love is cricket.
She too was found alive on the island.
"On day one I felt hungry but my appetite went away, but thirst kept growing. The only water I had was a mouthful of seawater that I swallowed when I was climbing the tree," said the boy from Nicobar's razed village Tapai Ming.
Murlitharan said he had been playing cricket with his pals on the morning of December 26 when the tsunami struck.
Doctors monitoring his health said they were baffled by his survival, adding the 21-kilogram (46-pound) child appeared to have lost nearly five kilograms of fluid and body mass during his ordeal.
"Whatever he has said about clinging to the tree for 10 days has been collaborated with a host of facts," said aid worker Sudhir Chakravarty, who is in charge of Murlitharan.
Murlitharan lost conciousness on January 5 and toppled out of the tree into mud left behind by the receding sea.
The boy, delirious, tried to reach his home, which has been wrecked, when rescuers found him. He was brought to the capital Port Blair on Thursday.
Friday after hearing news of his sister, father and mother, the boy recovered speedily and was in high spirits.
"I love to keep wicket and I am itching to play cricket with the gang here but they won't let me ... I hate geography and history but I enjoy maths, science and chemistry and (Indian batsman) Mohammed Kaif is my hero."
Aid workers said they were sheltering Murlitharan on the request of his father because of financial problems in Madras.
Almost 1,200 people are listed as killed, with 5,600 missing on the Andamans archipelago.
Some 44,000 survivors are housed in shelters on the Indian Ocean tropical chain of over 500 islands strung across 800 kilometres (500 miles) and located just east of Sumatra.