BBC Wales can reveal that Liverpool council is close to making a formal apology for the drowning of a Welsh valley almost half a century ago.
Party leaders on the city council have agreed the wording of an apology to go before the council on 19 October.
Tryweryn, near Bala in Gwynedd, was flooded in 1965 to create the Tryweryn reservoir to supply water to Liverpool.
The flooding displaced the small Welsh -speaking community of Capel Celyn and caused bitter political controversy.
An act of Parliament was needed for the compulsory purchase orders for the 800 acres and the legislation was pushed through even though no Welsh MP voted for it.
The scheme stirred up a cauldron of nationalist indignation and a desperate fight to save the 100% Welsh-speaking community.
"The drowning of the village of Capel Celyn in the Tryweryn valley was one of the most important political events in Wales in the twentieth century," said BBC Wales Welsh affairs editor Vaughan Roderick.
"When Liverpool Council announced its plans, they faced united opposition in Wales. Thirty-five of the 36 Welsh MPs voted against the plans and Tryweryn itself became the site of demonstrations and bombing attacks on construction equipment.
"The failure of the attempts to stop the plans led to a rapid growth in nationalism and calls for devolution and in the space of less than a year Plaid Cymru was transformed from a tiny pressure group into a major political party.
"It would not be an exaggeration to say that the road to the National Assembly for Wales began in Tryweryn."
Welsh assembly First Minister Rhodri Morgan has welcomed the proposed apology, describing it as a very good step.
And Plaid Cymru parliamentary leader Elfyn Llwyd told BBC Wales that the apology "should be accepted in the fulsome way it is being offered".
The failure to stop the plans led to a rapid growth in nationalism
"I am pleased it's come. It was a seminal moment in the history of Wales. It takes some guts to apologise and I'm pleased they have been able to do so.
"I hope they might take it a step further and contribute to a fitting memorial on the shores of the lake."
The resolution - to go before Liverpool's full council - will express remorse for the decision to flood the valley and for the insensitive way in which the matter was handled by the authorities.
It has come about a result of an intervention by the Liberal Democrat peer Lord Roberts of Llandudno who was saddened that Tryweryn was cited by many as a reason why the National Eisteddfod should not visit Liverpool.
His approach to the leader of the Liberal Democrat-controlled council led to the apology which is also backed by the Labour Party which controlled Liverpool at the time of the reservoirs construction.
Mike Storey, the leader of Liverpool council, said: "What happened to the people in the valleys was wrong and I think now is the right time to say sorry."