Whatever's in that vegan diet of his must not have any kind of negative impact on Paul McCartney's energy level, because the 72-year-old ex-Beatle seems to be everywhere these days.

As previously reported, McCartney recently raised eyebrows (and confused a few younger listeners) when he collaborated with Kanye West for West's new 'Only One' single -- and repeated the feat when he joined West and Rihanna for another new track, 'FourFiveSeconds.' With that out of the way, he's apparently moved on to some sort of project with Lady Gaga and Pearl Jam guitarist Mike McCready.

Gaga, who previously rubbed shoulders with greatness when she recorded an entire album with Tony Bennett, broke the news on her Instagram account, posting a series of photos and telling followers, "Had a beautiful session with Sir Paul McCartney and friends. Working on one of his many secret projects! Killer musicians, vibe and lots of laughs."

And for those of you who take offense at the notion of McCartney working with a performer who once appeared in public wearing a dress made out of raw meat, just know that it almost didn't happen. "I’ll never forget when he called me last year to work," wrote Gaga. "I hung up the phone cuz I thought it was a prank!"

We'll doubtless hear the results of the Gaga/McCartney/McCready summit soon. In the meantime, check out photos from the sessions below.

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