Kate Middleton Recovery Photo with Kids Released for UK Mother's Day

If Kate Middleton is a princess in pain, she's desperately trying to hide it by releasing a pic of herself smiling -- or grinning and bearing it -- surrounded by her 3 children.

The Princess of Wales posted the family pic Sunday in honor of Mother's Day in the UK. It's just the 2nd time we've seen Kate since her mysterious abdominal surgery in January ... and the first full-body shot since speculation about the procedure, her recovery, and her whereabouts have run rampant on the Internet.

In her caption, Kate writes, "Thank you for your kind wishes and continued support over the last two months. Wishing everyone a Happy Mother’s Day."

As we reported, the princess was photographed last week while out for a drive near Windsor Castle ... with her mother behind the wheel, and Kate wearing shades while in the passenger seat.

Of course, the fact we couldn't see her full body only fueled the outlandish social media rumor mill about her health.

Naturally, royal watchers are picking apart the new, more revealing pic, too. For instance, Kate is not wearing her wedding ring as she has her hands around her 2 younger children ... 8-year-old Princess Charlotte and 5-year-old Prince Louis.

The last time she attended a public event was on Christmas day, and yes, she was wearing it then. That fact won't help to quell one of the running theories, which involves speculation she and Prince William are on the rocks.

Then again, it could simply be the ring is off because she's experienced inflammation since her surgery.

One more note about the shot ... Kate is seated, as 10-year-old Prince George stands behind his mother. So, for those of you who have BBL on your "What's up with Kate" bingo cards ... we can't rule it out. Just sayin' ...