Most had believed they would put plans for a little one on hold due to Zika virus risks in the countries they travelled to, but the announcement was made shortly after they touched down in Australia.
Many people criticised the couple for sharing the happy news just a few days after Harry's cousin Princess Eugenie's wedding to Jack Brooksbank, with some even suggesting they stole her thunder.
But now the couple have revealed why they decided to tell everyone when they did.
During ITV's documentary about their massive tour, which featured 76 engagements over 16 days, Harry explained that they simply thought the location was perfect.
Speaking at Admiralty House on day one, the Duke said: "We're both absolutely delighted to be here and we also genuinely couldn't think of a better place to announce the upcoming baby, be it a boy or a girl. So thank you very, very much."