Multiple photo and new agencies -- like the Associated Press, Getty Images, etc. -- have yanked the picture in question, and AP even handed down a kill notification to journos worldwide ... letting them know they have reason to believe this photo may be manipulated.

Part of that message read ... "At closer inspection, it appears that the source has manipulated the image. No replacement image will be sent. Please remove it from all platforms, including social, where it may still be visible."

The hesitation follows a wave of skeptics online and elsewhere, who suggested the pic looked sorta AI-generated ... and did not at all seem authentic -- this despite the fact palace officials insisted it had been taken by Prince William himself at their cottage in Windsor.

On paper, this has been presented as the real McCoy -- but reputable news outlets are now distancing themselves and refusing to circulate it ... casting serious doubt on its legitimacy.

As of now, Royal officials have yet to comment on this, even to reporters across the pond ... and the photo is still on the Prince and Princess of Wales' official social media accounts.

If true, obviously it's scandalous ... and will only add fuel to the fire over Kate's condition as she continues to recover from abdominal surgery earlier this year ... which has sidelined her for a while. Photos of her that surfaced last week were also called into question.

Kensington Palace has attempted to tamp down rumors and speculation about all this -- but the Internet has been having a field day with memes, jokes and gossip regardless. This latest apparent Snafu ain't gonna help ... if anything, it'll kickstart a fresh wave of inuendo.