Gwent Police said the man was arrested in Hamburg on 12 August and will be extradited to the UK.
The man is believed to be Thomas Doran, who is wanted as part of Gwent Police's Operation Imperial - an investigation into serious offences against vulnerable adults on the Gwent Levels.
The extradition process can take six weeks, police added.

The proposal orders public bathhouses to display signs prohibiting "people with sexually transmitted diseases, Aids and infectious skin diseases".
It has been posted online for public consultation by China's State Council.
But Aids activists and ordinary users of Weibo, China's version of Twitter have strongly criticised the move.
"There is no evidence that people can be infected with HIV in public bathhouses," Wu Hao, from the Beijing Research Centre on Sexually Transmitted Diseases and Aids, was quoted as saying by the Beijing Morning News.
"Apparently, the rule to bar HIV patients from entering public bathhouses is way over the top," he said.
The paper also quoted an unnamed Aids activist as saying he was extremely disappointed with the draft proposal.
"Banning HIV patients from using public bathhouses and spas will only exacerbate people's misunderstanding, discrimination and fear of HIV/Aids, and will not help reduce the transmission of the disease," he said.
The proposal has also been condemned by the United Nations' Aids agency.
Hedia Belhadj, China country coordinator for UNAIDS, said it was concerned by the provision and called for it to be removed, the AFP news agency reports.
She said that there was no risk of transmission of HIV in a spa or bathhouse setting.
"UNAIDS recommends that restrictions preventing people living with HIV from accessing bath houses, spas and other similar facilities be removed from the final draft of this policy," Ms Belhadj told AFP.
The proposal has also drawn strong criticism from China's Weibo users.
One user said that the decision to ban HIV patients using public bathhouses must be based on scientific facts about the ways HIV was transmitted.
"In reality, many public bathhouses have already implemented the ban. The practice is discriminatory and must be stopped, and must not be institutionalised.
"HIV patients are already very vulnerable. They should be protected and respected. We must not further harm them with discrimination," the user said .
But there are also Weibo users who agree with the ban.
One Weibo user said that HIV patients should be advised not to use public bathhouses or at least they should check whether they have any open wounds before entering.
According to government figures released in 2012, China has 430,000 people infected with HIV.
But the United Nations has said that the real figure could be 620,000 to 940,000.
Among them, 146,000 to 162,00 have developed Aids.
A 60-year-old man from Cardiff has been arrested in Germany on suspicion of conspiracy to kidnap.
[NEXT_CONCEPT]
A government proposal to bar HIV patients from using public bathhouses has been condemned in China as discriminatory.