The twin brother of Polish President Lech Kaczynski has accepted the governing party's nomination to be the country's prime minister.
No other country has twin brothers in the top two jobs
Jaroslaw Kaczynski first turned down the job after last October's elections, saying it would be wrong for the brothers to hold the two top posts.
Saturday's decision came after current Prime Minister Kazimierz Marcinkiewicz tendered his resignation.
Mr Marcinkiewicz will stand for the post of mayor of Warsaw in November.
The post was held by Lech Kaczynski until he was elected president.
The development will make the Kaczynski brothers the world's only twins to hold the two highest posts in any country.
Marcinkiewicz has been PM since his party's election victory
Jaroslaw Kaczynski acknowledged possible problems with this.
"There is a certain risk for the president and prime minister to be brothers, that was the major roadblock," he said.
"But for various reasons, we came to the conclusion that, at this time, putting forward a different candidate - of which we have many good ones - would be a worse way out than recommending me.
"The party leadership put forward a proposal, and I accepted it."
However, media reports say three other parties - deriving both from the anti-communist Solidarity movement and the former Communist party - have signalled they will now form a coalition to counter the danger they say the two brothers would pose for Poland's stability.
Mr Marcinkiewicz will formally step down on Monday.
Over recent weeks, there had been frequent reports of a rift between Mr Marcinkiewicz and Jaroslaw Kaczynski over economic policy.
When the Law and Justice party won last October's parliamentary elections, Mr Kaczynski appeared to be the front runner to take on the role of prime minister, but he turned down the job.
At the time, his brother was due to participate in the second round of the presidential elections and Mr Kaczynski said it would be wrong for both brothers to hold the two top posts.
A former physics teacher, Mr Marcinkiewicz was previously the party's economic adviser head of the parliamentary treasury commission.