Björn Höcke called on Germans to take a more “positive” attitude towards their history in a speech last month, calling them a “brutally defeated people” who should stop attempts to atone for Nazi crimes.
Party leaders voted by the necessary two-thirds majority to open expulsion proceedings against Mr Höcke on Monday.
In a statement, she said she didn’t want Hitler to return “under any circumstances”, admitting she posted the images but insisting she did not condone them.
” Party officials said they were treating the allegations very seriously, forming a panel to investigate Ms Roon, although it was unclear whether she would be removed as an election candidate.
The move to expel him is being seen as an attempt at damage control as the Af D campaigns for Germany’s national election in September, where it hopes to enter the Bundestag for the first time.
“This is the conclusion of a process that has been going on for some time,” Frauke Petry, the party’s national co-leader said, accusing her rival of overstepping the mark of what is “democratically tolerable”.
“We think that this step was necessary because, in such an important election year, the party must be united.” Mr Höcke said he regretted the leadership’s decision but was confident about the proceedings.
In its short four-year history, the nationalist party has swung right from its original Eurosceptic ambitions to become known for its vehemently anti-immigration stance during the refugee crisis.
Immigration concerns and fears following a string of Isis-inspired terror attacks in Germany have stoked the party’s popularity, seeing it make unprecedented gains in last year’s local elections.