William was joined by King Charles and Queen Camilla who also shared a message of commiserations for the Aussie squad, as well as their heartfelt congratulations for their English team.
"My wife and I join all our family in sending the mighty Lionesses our warmest congratulations on reaching the final of the World Cup, and in sharing our very best wishes for Sunday's match," the monarch wrote.
"While your victory may have cost the magnificent Matildas their chance for the greatest prize in the game, both teams have been an inspiration on and off the pitch - and, for that, both nations are united in pride, admiration, and respect."
Prior to the match, The Welsh Guards Band also showed a "heartwarming display of support" for both teams during a changing of the guard ceremony at Buckingham Palace, the band playing both Sweet Caroline (the UK's unofficial soccer anthem) as well as Waltzing Matilda.
Whilst the Matildas won't be progressing to Sunday night's final against Spains' La Roja, they will be battling it out final time for third place against Sweden who were also knocked out after losing to Spain.
The match will stream live on Channel Seven and 7Plus this Saturday from 6pm.