AfD leader Frauke Petry, on the day after the German general elections | John MacDougall/AFP via Getty Images Frauke Petry won’t join AfD in German parliament Co-chair of far-right party drops ‘bombshell’ at press conference.

The Alternative for Germany's co-chair Frauke Petry announced Monday that she will not be joining her party colleagues in the Bundestag after the far-right AfD won around 13 percent of the vote in the German election on Sunday.

Petry appeared to take fellow party officials by surprise by announcing at a news conference that, "after long deliberation," she will not be joining the new party group. She then walked out of the press conference, leaving her colleagues baffled.

According to German press agency dpa, party co-chair Jörg Meuthen said he "had had no knowledge" beforehand of Petry's decision, which he called "a bombshell."

Petry was directly elected to a seat in Saxony on Sunday, where she was responsible for the AfD's strong showing, winning the largest share of votes.

Petry did not run as the party's lead candidate in the campaign to Sunday's election due to alleged differences over the party's direction. Party apparatchiks dismissed Petry's proposal for the party to adopt a "Realpolitik strategy" at a party conference in April, and chose former Goldman Sachs executive Alice Weidel and former conservative Alexander Gauland as the lead candidates instead.

André Poggenburg, the AfD’s group leader in the state of Saxony-Anhalt and also a member of the party’s executive board, called on Petry to quit the party.

“I encourage you to ... leave the party,” Poggenburg told DPA news agency. The AfD won 19.6 percent of the vote in Saxony-Anhalt, behind the CDU on 30.3 percent.