5/11 -- TMZ has learned the lawyer who handles Britney Spears' conservatorship has just been named Semel's conservator. Adam Streisand repped Terry's son in court Friday.
Terry Semel, the former Warner Bros. Chairman and Yahoo! CEO ... once one of the most powerful people in Hollywood, has been moved from his 13,000 square foot Bel-Air compound and warehoused in a 500 square foot apartment, and his son claims it's all the doing of Terry's wife.
Semel suffers from Alzheimer's and according to new legal docs, obtained by TMZ, Eric Semel says Jane Semel has been heartless, abusing her authority and not properly caring for his father.
Most concerning to Eric ... he says Jane has put Terry in the Motion Picture & Television Fund House, which he describes as "a retirement home intended for low-income entertainment industry members in Woodland Hills, CA."
Eric says Terry and Jane have homes in California, New York and London, and there is no reason "Mr. Semel should not be cared for and reside in a suitable, secured home that is accessible for his physical needs."
Eric is trying to wrestle power away from Jane and is asking a judge to appoint the lawyer who handles Britney Spears' conservatorship to manage his dad's affairs.