The BBC Scotland weather forecaster who wrote the script for Prince Charles's forecast only found out on Tuesday that the royal couple would tour the studio yesterday, as part of their visit to the BBC base in Glasgow.
"We were told it might be wise to have some weather graphics on standby in case they wanted to have a look and we also decided to write an autocue script. We don't normally use a script in weather - we just do it off the top of our heads," Blanchett added.
It was newsreader Sally Magnusson who asked the royal visitors, known in Scotland as the Duke and Duchess of Rothesay, if they would like to have a go at reading the weather before the lunchtime bulletin went on air.
Blanchett said: "Prince Charles seemed extremely happy about doing it so he just stepped in. I showed him where to stand, explained about looking down the camera and how to hold the clicker, and he was utterly charming."
Together with fellow forecasters Gillian Smart and Stav Danaos, Blanchett inserted special references to the royal residences in Scotland.
He said: "Prince Charles hadn't seen the script beforehand. He was just reading it as it appeared on autocue and quite enjoyed the royal references to Balmoral and Dumfries House. He realised [what we had done] as he was going through the script which is why he quipped 'Who the hell wrote this script'."
The video clip was the most popular item on the BBC News website yesterday and went viral around the world. It also led to Prince Charles becoming a trending topic worldwide on Twitter and BBC Scotland trending in the UK.
Blanchett says: "We sort of knew instantly this was television gold because I don't think a member of the royal family has done anything like this before."
The Duchess also had a go at presenting the weather after Charles, although her less impressive attempt was not shown live.
Sixty years and hardly a slip.