His death comes 2 years after he underwent life-saving heart valve replacement surgery -- he got a pig heart valve inserted in his chest, because his own had shrunk with age.
In his last interview in November 2023, he gushed his new heart valve was working wonderfully and told German newspaper Bild, he was grateful he had a "good pig in me."
Despite his claims of good health, contrasting reports said his condition had deteriorated after the procedure -- he'd lost a lot of weight and had to use a wheelchair and breathing equipment due to lung issues.
"Daddy Cool," "Rasputin," and "Mary's Boy Child" were just a few hits from the group comprised of Marcia Barrett, Liz Mitchell, Maizie Williams and Bobby Farrell.
His most dubious move, though, came in the late '80s ... Frank founded the R&B pop duo Milli Vanilli. He hired Fab Morvan and Rob Pilatus as the eye candy, while he enlisted other performers to do the actual singing on hits like "Blame It On The Rain" and "Girl You Know It's True."
The group would actually win the Grammy for Best New Artist before the whole lip-synching sham came crashing down during a "live" performance. The Recording Academy took back their Grammy.