Australia’s High Commissioner to the UK, Alexander Downer, may just have prompted Prince William to give the world its best clue yet as to the name of the his newly-born prince.

The Duke of Cambridge, who left his two-day old son with the Duchess to attend an Anzac Day commemoration service on Wednesday local time, has fuelled intense speculation thanks to a brief exchange with the former Liberal leader.

In reply to Mr Downer’s quip asking if the Prince had considered Alexander as the baby’s name, William replied: “Funny you should say that … It’s a good name.”

The Duke of Cambridge has fuelled speculation about the name of his new baby boy, telling a man who suggested he could suit Prince Alexander: "Funny you should say that…" pic.twitter.com/IVCsO9kZnL

— The Telegraph (@Telegraph) April 25, 2018

Royal watchers around the world, most of whom had no idea who Mr Downer was, were quick to jump on the exchange.

The comment has led Alexander to become the UK bookies’ new favourite, according to local media.

William also joked with the Dean of Westminster and Mr Downer’s New Zealand counterpart, Sir Jerry Mateparae, saying: “And Jerry would like it to be Jerry”.

“It’s a strong name, I have to say,” Prince William said smiling.

William was joined by Prince Harry and soon-to-be wife Meghan Markle at Westminster Abbey for the Anzac day service, but conversation with the now father-of-three was about the new Prince.

Prince William, Prince Harry and Meghan Markle leave after attending a Service of Thanksgiving and Commemoration on Anzac Day. Photo: AAP

The Duke provided updates on both Kate and his newborn son, saying they are doing “very well, thanks,”and that all parties involved are “in good form, luckily.”

“Sleeping’s going reasonably well so far, so he’s behaving himself which is good news.”

According to the UK Telegraph, the name Prince Alexander is not likely to be a final contender as it is one of Prince George’s middle names.