Heaven's Will

When a long-lost secret realm had been discovered by a small sect, three of the sects disciples decide to venture into it. Through sheer coincidences or luck, they were able to get past spells for warding off intruders, spirit beasts capable of killing them in seconds and complex puzzles no one would be able to think of. In the end, instead of heavenly treasures or secret techniques, what they found was a boy.

Who is this boy? What is his background? Why was he in the secret realm? Above all, did the three disciples really find him through coincidences? Or was it all through Heaven's Will?