Robson Thompson, 25, "eventually” admitted rape of and two counts of sexual assault against the boy following a police investigation.
He was sentenced to 12 years with an additional 5 years on license at Nottingham Crown Court on Friday.
Thompson, of no fixed address had pleaded guilty to sexually assaulting a young boy in Nottinghamshire at a previous hearing.
However he denied additional charges of sexual abuse of the same child.
Police say after a “thorough investigation” by detectives evidence found he had committed further offences.
Thompson later pleaded guilty to rape of and two counts of sexual assault against the boy.
Detective Constable Kerry Stringfellow, at Nottinghamshire Police, said: “Thompson’s monstrous acts were disgraceful, predatory and vile.
“He knew what he was doing was sick and wrong but carried on regardless, committing a number of offences over a series of months.
“While he handed himself in, he attempted to claim that he was not guilty of further offences. We were committed to ensure that we could secure guilty pleas.
“Sexual assaults are among the most horrific acts anyone can commit and we take investigations into such offences very seriously.
“We work hard to give victims appropriate support and I would like to commend the victim and their family in this case for their bravery in what is a traumatic and awful time.
“It is so important that victims and survivors of sexual assaults report incidents to police so that we can investigate them thoroughly.
“The sentence is the culmination of our efforts to bring justice and while it won’t erase what happened - I hope it brings some closure for those impacted on by Thompson’s actions.”
Thompson will be on the sex offenders register for life and subject to a sexual harm prevention order.