The commemorative event is held annually on the final Saturday in June to show its support for veterans, service families and cadets, as well as those still serving.
The new picture was captured last November in the Grand Corridor at Windsor Castle by Hugo Burnand.
The King, who is head of the Armed Forces, is wearing his Field Marshal No. 1 full ceremonial frock coat with medals, sword and a host of decorations.
Following the new release, fans have expressed their delight, with many saying that it is “much better” than another recent portrait of the monarch.
Taking to Instagram, where the Royal Family official account posted the new picture, one fan commented: “That’s a way better portrait.”
Another commented: “A much better portrait of Our Majesty The King [red-heart emoji].”
Comparing the new portrait to the red one released earlier this year, another fan commented: “Much better than the red one.”
A fourth fan wrote: “Great portrait [clapping-hands emoji] much better than that red painting. Long live The King [red-heart emoji].”
A portrait of King Charles by Jonathan Yeo was unveiled back in May and it attracted both praise and disdain.
The picture, which displayed a bright red background, showed the King in his Welsh Guards uniform with a butterfly about to land on his shoulder to symbolise his “metamorphosis”.
In a poll conducted by Express.co.uk which asked if fans liked the new red portrait, 2,551 (44.8 percent) said yes they did like the portrait, while 3,012 (52.9 percent) said no they did not.
Taking to X, one fan commented: “It’s different and I want to like it but the red is just too overpowering – maybe that’s the message?”
As well as comparing the new image to the red one, fans just appeared to love the new release.
One fan commented: “What a fantastic picture of Your Majesty [red-heart emoji].”
Another wrote: “Very nice portrait. I like the composition and colours in this portrait.”