Sad Panda News. Warning: do not read if you were planning on having a good Monday. (UPDATED)

We've got some absolutely heartbreaking news here at Panda Watch. The cub that was born last week to Mei Xiang, The National Zoo's giant panda, has died. Zoo officials report that more information is forthcoming, but, as of this morning, details surrounding the cub's sudden passing are sparse:

We are brokenhearted to share that we have lost our little giant panda cub. Panda keepers and volunteers heard Mei Xiang make a distress vocalization at 9:17 a.m. and let the veterinarian staff know immediately. They turned off the panda cam and were able to safely retrieve the cub for an evaluation at 10:22 a.m., which we only do in situations of gravest concern. The veterinarians immediately performed CPR and other life-saving measures, but sadly the cub was unresponsive.

UPDATE, 10:40 ET We just received this email from The National Zoo, detailing the preliminary results of the cub's autopsy:

We still don't know definitively what caused us to lose the giant panda cub yesterday, but we do have some more information since yesterday, especially from the necropsy (animal autopsy).

The giant panda cub appeared to be a female. She weighed a little less than 100 grams, which is about four ounces. There were no signs of trauma, external or internal, which means that she was not crushed-confirmation that Mei is a good mother. Her heart and lungs also looked good, which tells us that she did not suffocate. There was a little milk in the cub's gastrointestinal tract, which tells us that she did successfully nurse. The only abnormalities the veterinarians have detected so far were some fluid in her abdomen and a slightly abnormal liver. They don't know yet whether either of those things is significant, and they're still investigating.

In more uplifting conservation news: a beautiful, 7-foot long, 655-pound leatherback turtle was successfully rescued, treated for dehydration and released off the coast of Cape Cod this weekend. When it comes to preserving endangered species like giant pandas and leatherback sea turtles (the largest reptiles on Earth), it's impossible to win every battle — but a huge thanks to those who are doing their damnedest to safeguard them as best they can.