AT&T (T) - Get Report is losing subscribers across several platforms in the wake of the end of "Game of Thrones," one of the most popular television shows of all time, according to a KeyBanc Capital note. 

The company's AT&T TV NOW, DirectTV and HBO platforms experienced subscriber declines in October, according to an analysis of credit card data by KeyBanc analyst Brandon Nispel. 

While HBO subscriptions fell sequentially, the network still saw year-over-year growth of 57%, "likely due to season eight of 'Game of Thrones' in April." But KeyBanc also sees HBO's upcoming streaming service, HBO Max, as being "nowhere near as popular as Disney+."

Walt Disney (DIS) - Get Report launched Disney+ on Nov. 12, and the company reported that it already has 10 million subscribers. AT&T rival Verizon (VZ) - Get Report even has a promotion that gives certain customers a free Disney+ subscription for a year. 

AT&T shares were falling 2.5% Wednesday to $37.05.

AT&T also slid Tuesday after an industry analyst, skeptical of the telecom giant's ability to hit its 2020 revenue target, issued a rare sell recommendation on the shares.

MoffettNathanson downgraded the Dallas company's shares to sell from neutral.

The move became just the second sell rating from the more than 30 analysts currently covering the stock, according to Bloomberg.

AT&T's forecast for 2020, including 1% growth, "doesn't sound challenging," wrote analyst Craig Moffett, but "the more we poke at our estimates, the harder it is for us to imagine they can be achieved."

Moffett did affirm its $25-a-share price target on AT&T.