The first minister backed the renaming of the Second Severn Crossing to the Prince of Wales Bridge months before it was officially announced, a freedom of information request has revealed.
The UK government announcement in April stirred controversy over whether there should have been a public consultation.
Initially the Welsh Government said that it had raised no objections.
But a letter shows Carwyn Jones offered more support than that, offering to take part in the renaming ceremony.
The crossing is being renamed to mark 50 years since the Prince of Wales' investiture in Caernarfon in 1969, and coincides with the transfer of the two Severn bridges to public ownership and control under the UK government.
In April, a Welsh Government spokeswoman said: "Alun Cairns [the Welsh Secretary] wrote to the FM about the naming of the bridge last year and we didn't raise any objections."
Later, Economy Secretary Ken Skates was more positive, saying many supported the renaming.
But a Freedom of Information (FOI) release following a request by BBC Wales to the Wales Office shows that months before the announcement the first minister had gone further than simply not raising objections.
"I welcome the idea to rename the crossing the Prince of Wales Bridge," Mr Jones said in a letter to Mr Cairns last December.
"The Welsh Government will support the proposal and I stand by to be involved in the formal renaming ceremony."
As well as Mr Jones' letter, the correspondence shows that Mr Carins had written to Mr Jones about the proposal back in March 2017 - 13 months before the official announcement.
"I have long been of the opinion that [the] title of 'Second Severn Crossing' is not fitting for the main gateway to Wales from the South West [of England]," Mr Cairns wrote.
Mr Cairns wrote that the UK government intended to rename the crossing "in honour of the significant contribution that the Prince of Wales has made to our nation".
The FOI release includes two further letters from Mr Cairns to Mr Jones - 24 September and 6 December last year - asking for his views on the plan.
The second letter states that St James' Palace was asking for "clarity" that the Welsh Government supported the initiative.
"I am now in a position where I need to be able to let the Palace have a clear steer. I do hope you will feel able to write back in supportive terms," Mr Cairns wrote.
Mr Jones' reply - which thanks the Welsh secretary for his September letter - was written on the same day as Mr Cairns's second request.
The Welsh Government has been asked to comment.