The prime suspect in Madeleine McCann’s abduction once sexually abused an ex-girlfriend’s five-year-old daughter — and was busted after explicit photos were found on his laptop, according to a report.

Christian Brückner, 43, assaulted the youngster in a public park in Braunschweig, northern Germany in 2013 and took graphic photos at the scene, officials told the Mail on Sunday.

They were then found when he was accused of domestic abuse against a different ex — and the disgusting child abuse images were discovered by police who searched his laptop and other devices, the paper said.

Brückner — called Christian B. by authorities and whose surname is also sometimes spelled Brueckner — had already returned to Portugal, the country where McCann went missing in 2007 at age three.

German authorities issued an EU-wide arrest warrant, the UK paper said.

But he was not arrested in Portugal for another four years — busted after he was accused of exposing himself to kids in a park about 40 miles from where McCann was abducted, the report states.

Brückner was extradited back to Germany and given a 15-month prison term after being convicted in 2017, the Sunday paper said, citing Hanover’s chief prosecutor, Thomas Klinge.

He has also been convicted of the 2005 rape of a 72-year-old American tourist in the same Portuguese resort where Maddie went missing — but has yet to start his seven-year sentence while it is being appealed.

Brückner was already in prison on drug charges when he was named as the prime suspect in McCann’s disappearance, the biggest missing children’s case in recent history.

Officials have previously claimed they now have “concrete evidence” the British youngster is dead — but Brückner’s attorney has reportedly declared his confidence that his client will never get charged.

That attorney, Friedrich Fulscher, declined to comment on the Mail on Sunday’s report. Brückner has always denied taking McCann.