AT&T shareholder Elliott Management on Monday questioned the wireless carrier’s $85 billion takeover of Time Warner and called for it to sell non-core businesses to boost its stock price, driving shares in the company up 10 percent.

The hedge fund group, one of the United States’ best-known activist investors, called the telecoms group “deeply undervalued” and said with the right changes over the next two years, it could be worth almost double its current share price.

Elliott, which has an interest in AT&T together worth about $3.2 billion, gave a list of possible businesses the group could sell to generate funds without listing any of its Time Warner assets.

Shares of the company, which closed at $36.25 per share Friday, rose 10 percent in trading before the bell.

“Despite nearly 600 days passing between signing and closing (and more than a year passing since), AT&T has yet to articulate a clear strategic rationale for why AT&T needs to own Time Warner,” Elliott said in a letter to the company’s board of directors.

“AT&T can unlock significant value by focusing its asset portfolio, improving operational performance, instituting clear capital priorities, and enhancing leadership and oversight.”

President Donald Trump, who questioned the Time Warner deal while it was being examined by US regulators, welcomed the intervention of Elliott and called for it to make changes at its CNN network.

Elliott, which oversees $35 billion in assets, has waged successful campaigns for major change at firms including eBay, software firm SAP and Telecom Italia. It said its investment in AT&T was its largest ever.