Olivia Newton-John (as Sandy) and John Travolta (as Danny) in 1978's 'Grease.' — Paramount Pictures/Fotos International/Getty Images

AARP: John is something of a revelation on this album.

Newton-John: Isn't he!

AARP: You really dust off those tenor pipes. Olivia, did that surprise you?

Newton-John: I knew John had distinctive sound, 'cause I've heard him when we were messing around. I think this album is going to surprise people. He has a really great style.

Travolta: Oddly enough, because I started on Broadway, I probably had more vocal training than I did dance or acting. My mother was a singer, and we started early with that stuff.

AARP: Sometimes on duet albums you get a sense that two people have been slapped together and it's,"Well, let's get this over with." But really, you're bringing something else to this album, aren't you?

Travolta: Yes!

Newton-John: (Fondly) Yeahhhh. It was a work of love for us. It was John's idea to do the Christmas album. Last year, when they announced that our duet, "You're the One That I Want," was the top-selling duet record in history, I sent John a text to congratulate him. He suggested this album, and I said, "Why don't we do it to benefit our charities?"

Mine is the Olivia Newton-John Cancer and Wellness Centre in Melbourne, Australia. It's a brand-new cancer center with a wellness center attached to it, which has been my dream for many years, since I went through breast cancer and realized the importance of other healing modalities.

Travolta: And my side goes to the Jett Travolta Foundation [named for Travolta's son, who had autism and died of a seizure in 2009]. I was lost when I lost Jett. I didn't know what to do. One of the things I decided to do was to put a lot of money into seizure research, and a lot of money into autism schools and the like. The Jett Foundation also makes donations to handicapped Olympics and arts. Donating the proceeds also motivated our friends to join us making the record. Because when they knew it was for this incredible hospital that Olivia started and for my son, whom most of them knew, they just felt that it was the right thing to do.

AARP: By "friends," of course, you mean Barbra Streisand and Cliff Richard, and Tony Bennett and James Taylor and Kenny G and Chick Corea. All of them are on the album. That's quite a guest list you've got there.

Travolta: I have to agree. Even I'm impressed! (They both laugh.)

Newton-John: And with a Christmas album, we can raise money every year.

Travolta: Right! I'm still listening to my Johnny Mathis 1960 Christmas album. I hope in 50 years this'll be around, just like that. This and Grease. (Laughter)

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