Robert Wiles, 50, and Pauline Carr, 72 have both been jailed for crimes they committed in the 2000s.
Wiles, from Peterborough, sexually abused a young girl for five years between December 2004 and September 2009.
It also transpired that Wiles ill-treated a young boy with Pauline Carr, his ex-partner's mother.
The paedophile's offending came to light in December 2018, when his first victim bravely came forward to Cambridgeshire police to report the abuse.
Wiles, of Bringhurst, Orton Goldhay, Peterborough, faced Peterborough Crown Court on Monday, March 25.
There, he was sentenced to 20 years in prison having been found guilty of two counts of assaulting a child by touching, three counts of assaulting a child by penetration, five counts of raping a child and one count of ill-treatment of a child.
Carr, of Wildlake, Orton Malborne, was jailed for two years and three months, having been found guilty of ill-treatment of a child.
DC Annette Renwick said: “Robert Wiles shamefully took advantage of a vulnerable child to sexually abuse her so I am delighted he is behind bars for many years to come.
"Pauline Carr displayed despicable behaviour towards a child and caused suffering no child should endure.
"Each victim has suffered a great deal of emotional and psychological trauma as a result of the abuse they have been subjected to.
"They have both shown great courage and strength to come forward with their complaints to support police with a prosecution and then appear in court to give evidence.
"Their bravery is admirable, and I hope this sentencing can bring them and their families some sense of closure.”
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