When Mark Woods realized he had to say goodbye to his beloved 18-year-old whippet Walnut, he put out a call on social media.

He was hoping that friends and their dogs would join them for one last walk on his pet's favorite beach near Cornwall in the United Kingdom.

His Facebook post read:

"Sadly I am having to have Walnut euthanised on Saturday 12th November and so we will be having a last walk together on his beloved Porth Beach at 9.30am. I would love it if dog lovers/owners and friends would join us for a celebration of Walnut on his favourite Porth Beach. He has had an incredible life and having reached the grand age of 18 is ready for his final sleep. Hope to see you on Saturday."

Instead of just a few family and friends and their pooches showing up, the post went viral. Hundreds of people — many of them strangers — came to support Woods and Walnut. More than 19,000 people reacted to the post from all over the world and many pledged to walk their pets at the same time, wherever they were, in a show of support.

After the final walk on the beach, Walnut was put to sleep just before noon that day, surrounded by his human and canine family, including fellow whippets Monty, Nelson and Charlie.

"He went very quickly and in my arms," Woods wrote on Facebook. "I am writing this post because I owe it to everyone who has supported myself, my family and most importantly Walnut. Thank you to the hundreds of people that attended the walk this morning and to all those that had their own walks with their beloved pets at 9.30am all around the world."

Here's a touching video of the pair's final walk, as they were joined by hundreds of friends and strangers:

After the walk, The Ethical Record Label released the song "Walk with Walnut" with all record sales going to the Battersea Dogs and Cats Home animal rescue group.

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.