'All of Me' is the first R&B ballad to crown the Adult Pop Songs chart in 18 years. Notably, it's the first R&B ballad to rule Adult Pop Songs since Mariah Carey and Boyz II Men's "One Sweet Day" (a fellow Columbia Records release).

What's brought an unhurried R&B song back to the summit at a format historically known for its pop/rock lean? (Maroon 5, Katy Perry and P!nk share the mark for the most Adult Pop Songs No. 1s, with eight apiece. Nickelback follows with five.)

"The track has a singer-songwriter feel to it," says Matt Sparker, music director at Adult Pop Songs reporter KQKQ Omaha, Neb. "Yes, ['All of Me'] is R&B, but our audience doesn't shy away from slow, piano-driven songs. It isn't too far away from what they already like, but still different enough to stand out."

"I think it comes down to a song-by-song basis every time, and this particular song is just that special," says KLLC San Francisco MD Jayn. "It doesn't matter what format John Legend was previously known for."

Helping aid Legend's coronation is a recent invasion of R&B-flavored hits at the format from the likes of Justin Timberlake and, via multiple smashes, Pharrell Williams. (Some stations are also playing an uptempo Tiesto remix of "All of Me.") "The music cycle we're in allows this," theorizes KHMX Houston program director Bob Neumann. "There's the Pharrell factor, which can't be denied. ['All of Me'] fits like a glove. And, it's just a great song."

While "All of Me" has ruled two other radio charts, Adult R&B Songs (for seven weeks in February/March) and Pop Songs (for three weeks running), its ascent to the Adult Pop Songs summit was less widely envisioned. "I'll admit I was skeptical at first about the song," says WVMX Columbus, Ohio, assistant PD/MD Joe Kelly. "Slower songs can often struggle in a format where energy is tops. But, there is an amazing energy to this song that comes from emotional lyrics that connect."

Kelly echoes that the adult pop format has accepted more rhythmic hits of late. I.e., the title of Robin Thicke's "Blurred Lines," which topped Adult Pop Songs for six weeks last year, serves as a metaphor for the mix of genres that the format's programmers now find more acceptable. "As with any pop-driven format, you have to be in tune with listeners' expectations. So, when those expectations grow and change, so must we. What was expected and accepted a year ago is different than today.

"'All of Me' is simply a beautiful song and performed with grace," says WVMX operations manager Jimmy Steele.