The BBC has no ambitions for a takeover of S4C when it starts to fund the channel, says the BBC Trust chairman.
In a letter to his counterpart at S4C, Sir Michael Lyons said the BBC was committed to maintaining the channel's creative independence.
As part of the UK government's Spending Review last month, the BBC will take over funding within three years.
Legislation has been introduced to break the link between the channel's annual grant and inflation.
In his letter to S4C Authority chairman John Walter Jones, Sir Michael said that in 2013/14 the BBC will contribute more than £76m to the channel.
He said: "The BBC Trust is the guardian of the licence fee and as a result will need to have oversight of how this money is being spent.
"The licence fee settlement sets out in broad terms how this might be achieved."
He added: "I want to be clear with you, and other members of the S4C Authority, that the BBC has no ambitions to take over S4C.
"We are committed to a creatively independent S4C, which attracts revenue from a range of sources, including the licence fee.
"We share your determination that S4C should retain its strong relationship with the independent production sector in Wales."
The changes to S4C's funding has sparked a political row, with the leaders of Wales' four main parties recently writing to Prime Minister David Cameron to ask for an independent review of the channel's future.