Playboy Mansion: Last Grammy Dance in the Grotto?

Diddy will be holding court at the Playboy Mansion right after the Grammys ... and there's a decent chance it will be the last party of its kind at the legendary spot.

Anyone can attend the charity event called the City Gala -- for a $1,500 minimum donation -- where Sir Richard Branson and ex Playboy covergirl Jane Seymour will share the stage with host Diddy.

Aside from an open bar and a buffet, you can also catch a celeb poker game with Carl Weathers, John Salley, Tito Ortiz and Omar Benson Miller.

Remember, the Bunny palace is now on the market ... so it's possible it won't be owned by a party animal like Hugh Hefner when the 2017 Grammys roll around.

Ticket to hang with celebs -- $1,500.