The 94-year-old was clearly delighted to learn that the climate-sceptic Republican candidate would no longer sit in the White House, and hopes that the USA can lead the rest of the world in setting an example with regards to the environment.
Joe Biden immediately vowed that he'd sign America back up to the international agreement to limit global warming.
That's good news for us all, not just for Attenborough and the USA.
Sir Dave explained: "America is the most powerful country in the world, economically, and has huge influence on what happens.
"That someone should be coming into power who recognises the importance of the ecological problems that face us - whose first statement after it became clear he was going to become the President Elect was to reinstate America's backing of the Paris agreement...
"I can't remember getting out of my seat and cheering all by myself until that moment."
He continued: ""I have never done it before, even for our own elections.
"But when I heard that I actually said... [at this point, he apparently jumped out of his seat and started mouthing the word yes whilst raising his arms]"
Even though Trump is set to leave the US Presidency on January 20 - provided The Donald doesn't kick up a stink about it - there's still a lot of work to be done if we're to reverse or even stop the advancement of climate change.
With that in mind, Attenborough has created yet another documentary series called A Perfect Planet that will air on BBC One next month.
The first few episodes of the series will look at things like the weather, biodiversity, ocean currents, and things like that, but the fifth episode will be a sharp about-face to assess what impact humans have on the planet.
Without spoiling it - we've not seen it yet either - it's probably not going to be good news.
Speaking ahead of that series, executive producer Alastair Fothergill said that the reaction to the coronavirus pandemic has actually provided a source of hope.
He said: "We've seen how, in the search for the vaccine, humanity has united and put so much energy into solving that problem.
"To be honest, Covid is a relatively small problem compared with the planetary crisis facing us. So if humanity can unite to solve Covid surely we can to solve climate change?"
Attenborough hopes that change can begin with a new face in Washington.
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