FOX - Why did Fox stock slump today? The big Fox-News recombination plan

Stock in broadcaster Fox pulled off its worst day in more than 2.5 years Monday - ( NASDAQ: FOX ) -8.1% , ( NASDAQ: FOXA ) -9.4% and easily the worst performer among big Communications stocks - as investors reacted for the first time to weekend news that the company is studying re-merging with its former media sibling News Corp .

For its part, News Corp. stock rose Monday (( NASDAQ: NWS ) +2.5% , ( NASDAQ: NWSA ) +3.4% ).

Fox and News Corp. and their various holdings used to be part of the same empire under Australian mogul Rupert Murdoch. That includes assets currently held by the two companies (Fox's broadcast networks, Fox News, Fox Business, Tubi streaming, Dow Jones and The Wall Street Journal, publisher HarperCollins and many more) as well as media assets that Fox eventually sold to Disney.

The companies split up in 2013, with News Corp. becoming mostly a news publishing and real-estate services company.

Now Murdoch - whose family trust still owns about a 39% voting stake in News Corp, and a 42% voting stake in Fox - is looking at bringing what's left of the empire back together, with boards at each company studying the feasibility.

Analysts aren't yet seeing the value of a re-merger for the Fox side of the equation, though. Morgan Stanley's Benjamin Swinburne says the idea to bulk up may be coming from Fox's low multiple with some secular media headwinds building up - but that it won't help linear TV, where Fox derives most of its earnings.

And Credit Suisse's Doug Mitchelson says the former investment pillars for Fox have been blunted as the market turned, and the remaining one - Fox's $5B in cash - is undercut by a move to re-merge.

Activist investor Irenic Capital Management is reportedly pushing for News Corp. to split off its real estate listings business from its media operations .

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