Pharrell cries over 'Happy' with Oprah

You've heard the infectious song over and over.

Happy is Pharrell Williams' No. 1 hit.

And on Sunday night, Oprah Winfrey sat down with the singer on Oprah Prime and he talked about how — "boom" — the song exploded when the video arrived last November.

She asked him to take a look at a montage of fan videos from around the world, featuring people dancing and singing along to the upbeat tune. Dakar, Germany, Malawi ...

It reduced the singer to tears. And now the touching clip is trending on Facebook, two days later.

"Makes me cry, too!" said Oprah as Pharrell wiped tears away. She offered him a Kleenex. "I know. It's beautiful."

She said, "It's being used for something greater than yourself. I get that."

He said: "It's overwhelming, because it's like I love what I do, and I just appreciate the fact that people have believed in me for so long that I could make it to this point to feel that."

Sweet moment. Sweet interview.

Wise Oprah then said, "I so now get why it's so infectious — because it came from such a clear space that the energy was absolutely uninterrupted by anything than allowing it to flow from heart to heart."