When is the bitcoin reward provided to the miner? The rewards are provided to the miner if the miner finds a valid block. So Is the rewards(new bitcoin 12.5 + transaction reward) provided to the miner as soon as the new block is found by miner or reward is provided only when validated by other miners?

If reward is provided as soon as block is found, what happens in case of fork created. ?
The reward is just a transaction which payers the miner, called a Coinbase transaction. Thus it only pays the miner if that transaction is in the accepted blockchain, i.e. if it was invalid or if another block was found first that block would not be included so the miner would not be paid. In fact coinbase transactions only mature after 100 blocks have been mined on top of them, to avoid miners spending coins straight away and then a reorg happens and the block becomes a fork