Keith Meister's Corvex Capital has taken a large take in Yum Brands, sources told CNBC.
Corvex is now one of Yum's top five shareholders, purchasing shares early in the first quarter of 2015, according to sources. Meister will offer more details about his investment on Monday at the IRA Sohn Conference.
Meister bought Yum stake earlier in the first quarter, according to the sources.
Shares held their sharp gains.
While Loeb is bullish on the U.S., he noted that Third Point had "invested in more single name shorts this year than in all of 2014 combined," the letter said, referring to bets he made against some companies.
The letter said the firm was "constructive" on the U.S. because of improving economic data and the likelihood of continued low interest rates.
"These factors should create an environment where growth improves and monetary policy stays flexible, which is generally good for equities (higher multiples notwithstanding)," the letter said. "We may follow last year's playbook and ignore the old adage to 'sell in May and go away.'"
A spokesman for Third Point declined to comment. The firm manages about $17.5 billion. Its main fund is up 3.8 percent net of fees through April, according to performance information obtained by CNBC.
Loeb said his hedge fund's new position in Yum was "significant."
He wrote that the KFC and Pizza Hut-owner was in the "early stages of turning the page on recent troubles" in China.
That development, Loeb said, "should neutralize the largest overhang on the stock, set the stage for a dramatic profit recovery over the next 12-24 months, and change the public market narrative around long-term shareholder value-creation for the company."
"We appreciate their confidence and investment in Yum Brands," a company spokesperson said via email.
On Devon, Loeb wrote that the "value proposition is compelling."
"Devon stands out by combining limited downside with an under appreciated, valuable asset base that can be unlocked through continued portfolio management and improved operations," the letter said about the Oklahoma City-based oil and gas company.
Devon's stock was up slightly by late morning.
The letter also noted Third Point was even more bullish on Japan, thanks to corporate governance reform.
"Abe identified corporate governance reform as a key element of his "Third Arrow" and while it took its time hitting its target, it is in full bloom this Spring," the letter said, referring to Japanese Prime Minister Shinzo Abe.
It said the firm now has nearly 10 percent of assets invested in the country. Current holdings include Fanuc, "the Apple of Japan," according the Loeb, and IHI, a broad-based manufacturer.
—CNBC's Kate Kelly and Scott Wapner contributed to this report.