Six opposition parties in Hungary are coming together in a historic bid to oust long-time prime minister Viktor Orban.

       They will unite behind one candidate to challenge Orban in Hungary's parliamentary election, which is scheduled for next year.

       Orban, who leads the Fidesz party and has been prime minister since 2010, has won three successive elections.

       Later this month, opposition parties will hold a primary to choose a candidate. A second round is expected to take place at the beginning of October. The winner will be supported by the opposition parties in the 2022 election.

       "It's a huge milestone," said Róbert László, an expert on Hungarian elections from Political Capital, told Euronews.

       "Nothing like this has ever happened before in Hungary.

       "We've known the Fidesz party's electoral system since 2011, but opposition parties were nowhere near this kind of comprehensive collaboration before the elections of 2014 or 2018."

       "The primary is part of this new cooperation between parties.".

       "This is definitely a risky development for Fidesz. The party's earlier policy was to divide the opposition in the hope that they won't be able to work together. But now it turns out that they can cooperate.

       "It wasn't just because of the primary. Parties were already willing to cooperate. And the primary is just a consequence of that," László added.

       Watch the full report in the video player above.