The Fleetwood Mac singer, who dedicated a performance of her hit 'Landslide' to the on/off couple after they attended her concert in Las Vegas last month, wants the duo to get married and thinks they are the perfect couple because they are so different.
The 65-year-old star told UsMagazine.com: ''They seem to be a really great couple, and they seem to really care about each other. I am just hoping for the best for them. It would be great if that relationship really worked out and they were together forever. I think they're really good for each other. They're very different people, and that's the best way to go out with somebody. I always love to dedicate 'Landslide' to people I know really get it and appreciate it. Because it doesn't go out to anybody.''
Stevie also revealed that she became a huge fan of the 29-year-old 'Roar' hitmaker's long before they met and she has a lot of respect for 'Wildfire' singer-songwriter John, 36.
She explained: ''I like Katy's songs and her energy. I dance to them and I treadmill to them. Anybody who makes my treadmill list is my friend because they are helping me to keep my weight exactly where I want it to be. I think Katy's really fun, funny and quirky. I met her in London months ago. We sat down at 11:30 at night. We sat in the coffee shop for three hours. We ran the gamut of her life, my life and everything. I just really like her.''
She added: ''And I have been friends with John Mayer for a long time. I think John Mayer is one of the finest songwriters ever. He is right up there with James Taylor, Don Henley and those people. I really love him and respect him for those beautiful songs.''
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The singer has donated half a million to relief efforts.
Pratchett died aged 66 in March 2015.