The golden touch of Russian investor Yuri Milner, who made a killing on Facebook, apparently doesn't extend to Silicon Valley real estate.

The Santa Clara County assessor said Tuesday that the Los Altos Hills mansion the Russian billionaire paid $100 million for last year is worth a mere $50 million.

The mansion's purchase, through a limited liability corporation called LaPaloma Property, made headlines last March as the largest amount ever paid for a home in the U.S. Perched on a hill in Los Altos Hills, the 17-acre estate has a commanding view of the Bay Area.

Assessor Larry Stone said Tuesday that the house has a fair market value of $50,270,000,

(Google Map)
following an extensive survey of other mansions as far away as Beverly Hills.

Did Milner pay too much for the lavishly appointed mansion?

"'Overpaid' is relative and judgmental," Stone said. "He paid more than the fair market value."

The assessment means a big property tax break for Milner -- about $600,000 in taxes instead of $1.2 million. But that may come as a disappointment to local school districts and the town of Los Altos Hills, which will receive less tax revenue. Stone scheduled a conference call Tuesday with the two local school districts and town officials to explain how the fair market value of the home was determined.

The valuation doesn't have anything to do with the troubled housing market in other parts of the Bay Area because home prices have soared in the upscale parts of Silicon Valley along the Peninsula. But, even at $50 million, the property will probably drive prices up on surrounding estates.

If Milner's real estate acumen seems shaky, his other investments more than make up for it.

Milner has been an early investor in several hot Silicon Valley startups. One of his former companies in 2009 bought 44 million shares of Facebook for just $4.54 a share. Facebook was selling for about $31 a share Tues

Forbes estimated Milner's worth$1 billion. earlier this year.

His Los Altos Hills home, one of the largest in Silicon Valley, is a 25,545-square-foot mansion that features a ballroom, game room, maid's room, library, two dining rooms, an indoor pool, sauna and spa, two three-car garages, a carwash, tennis courts and 14 bathrooms. There's also a 4,613-square-foot guest home.

Comparable mansions have sold for less, according to the assessor. For example, a 30,000-square-foot mansion on 7.5 acres in Los Altos Hills sold for $28.5 million, and a 38,849-square-foot mansion on 6.7 acres in Woodside was listed at $43 million. The much larger, 56,500-square-foot Aaron Spelling Manor in Los Angeles sold for $85 million in July 2011.

"The law is very clear that assessors must assess property at its fair market value," Stone said. "We are not handling this transaction any differently than we would a condo in East San Jose."

Some of the top sales and listings in Santa Clara and San Mateo counties, which were used to help determine the value of the Los Altos Hills mansion:
30,000 sq. ft. mansion on 7.5 acres in Los Altos Hills -- sold for $28.5 million
18,000 sq. ft. estate on 4.8 acres in Los Altos Hills--- sold for $25 million (listed for $31 million)
11,000 sq. ft. historic mansion on 12 acres in Atherton -- sold in September 2001 for $53 million
Largest Estate Listings
38,849 sq. ft. mansion on 6.7 acres in Hillsborough -- listed for $43 million
14,000 sq. ft. estate on 4 acres in Woodside -- listed for $43 million (just canceled)
35,000 sq. ft. estate on 5.9 acres in Hillsborough -- listed for $29 million
16,000 sq. ft. mansion in Pacific Heights area of San Francisco -- listed for $28.5 million
5,850 sq. ft. estate on 3.4 acres in Woodside -- listed for $19 million
8,285 sq. ft. estate on 11.61 acres, Portola Valley -- listed for $25 million
13,459 sq. ft. estate on 7.88 acres in Saratoga -- listed for $16.7 million
56,500 sq. ft. Aaron Spelling Manor in Los Angeles -- sold July 2011 for $85 million
Source: Santa Clara County Assessor's Office