Many thought it was for Diana.

But there's actually another reason why Kate Middleton appeared in a red and white dress today. As well as celebrating the birth of her new baby boy, the UK is also celebrating St. George's Day, and just like wearing green for Saint Paddy, red and white is usually worn for St. George. The holiday is celebrated by various Christian Churches and by the several nations, kingdoms, countries, and cities of which Saint George is the patron saint.

Kate Middleton wears red and white her #RoyalBaby3's debut in honor of St. George's Day! pic.twitter.com/9oqocwAAnU

— InStyle (@InStyle) April 23, 2018

St. George’s fame took off in England after the return of the knights from the Crusades, with tales of St. George appearing in front of them at Jerusalem in 1099. Many believed that Kate wore red and white to honour William's mother Diana.

Kate wearing red is a lovely nod to Diana’s outfit when she left the hospital with Prince Harry #royalbaby❤️ pic.twitter.com/jBoDIySfjF

— Lexy Rose Illustration (@lexyroseart) April 23, 2018

Diana also wore a very similar dress when she greeted the world after Prince Harry was born. The introductions happened a lot quicker for baby number three as just moments ago Kate Middleton and Prince William left the Lindo Wing with their new baby boy. In the last hour, William had arrived back at the hospital with Prince George and Princess Charlotte to introduce them to their new brother, and now the world is getting the same opportunity.