They say that friends become your family when you get old. Presenting Exhibit A.

Taking care of older friends and family can be hard work, but it can also be rewarding.

Meet Donna, Nicki, and Bill. They're lifelong friends, and as one of them nears the end of life, they've become family.

From the love of opera music ("20 million albums!") to the simple joys of life (like finding the best soup in town), these two ladies are helping Bill make it through, one day at a time.

"All that really matters is shelter, food … and if you get to have friends, how lucky you are!" All images via AARP and Ad Council.

Bill had a stroke while at the opera with Donna and has been more frail since then. But Donna and Nicki are up for the challenge — helping him try to walk every day, listening to opera with him, and navigating the daily struggles that living with the after-effects of a stroke can present.

Caregivers like these are people to cherish, and they've made it their passion to help Bill be as comfortable as he can at this stage of life.

It's clearly something they love doing and wouldn't trade for anything in the world.

But folks who take care of others are often the uncelebrated, behind-the-scenes people in our culture.

As for Bill, he definitely celebrates these two:

"They're gorgeous; they're smart; I enjoy them immensely. It's almost overwhelming to list their virtues."

"It's a wonderful world, and I'm happy to be in it still," says Bill.

Caregivers are a vital part of our society, and they're also often working full- or part-time jobs while balancing these demands.

It's a labor of love, certainly, but it's also frequently a hidden part of what people do. Check out more of this sweet story of this unusual yet crucial relationship here:

Some facts, all from the National Alliance for Caregiving and AARP:

1. Nearly one-fourth of all of America's caregivers are millennials (ages 18—34), and they're equally likely to be male or female.
2. The value — that is, if it were paid — of caregiving by family members was approximately $470 billion per year in 2013.
3. About 40 million family caregivers help another adult or loved one carry out daily activities.
4. More than half (55%) of family caregivers report being overwhelmed by the amount of care their family member needs.

We need to celebrate people like these every chance we get.

This clip is by Ad Council/AARP.