'Frasier' Star David Hyde Pierce Flips L.A. Mansion for MASSIVE Profit

Take note, Michael Phelps -- "Frasier" star David Hyde Pierce knows how to play the real estate market ... because the actor just dumped his massive L.A. mansion for nearly DOUBLE what he paid.

Sources tell TMZ, Pierce listed the gated 8,184 sq. ft. Los Feliz home back in April for $7.5 million -- and it sold July 31st for $7,050,000. We're told it was the highest-priced sale in the neighborhood in recent memory.

But that's not the craziest part -- Pierce purchased the 7-bedroom 8.5-bathroom home back in 2003 ... for a mere $3,625,000 ... meaning he nearly doubled his investment in 9 years.