Shares of WW International Inc, also known as WeightWatchers, slumped more than 12% before the bell on Thursday after the weight-loss program operator said its top shareholder Artal Group S.A. had sold its remaining stake in the company in a block trade.

Market sources told Reuters late on Wednesday that a block of about 14.8 million shares was being marketed at about a 13% discount to Wednesday's close of $8.30.

The stock was last trading down 12.7% at $7.25, after more than doubling in value this year, partly due to Goldman Sachs' bullish call in April on expectations that the firm's entry into the obesity drug business will help drive a turnaround.

Artal Group held an 18.8% stake in the company at the end of December 31, according to Refinitiv data.

Luxembourg-based investment manager Artal bought WeightWatchers from then H.J. Heinz in 1999 for $735 million.

Anne Goffard, managing partner of Artal did not immediately respond to Reuters' request for comment.

WW International shares soared in 2015 after media mogul Oprah Winfrey joined Weight Watchers' board and took a 10% stake in the company.

The company reported $211 million in first-quarter revenue last week, an 18% drop from a year earlier, while the net loss widened to $118.7 million from $8.2 million.

(Reporting by Medha Singh in Bengaluru and Lance Tupper in New York; editing by Eileen Soreng)