Wendy’s Co. shares rallied in the extended session Tuesday after Nelson Peltz’s activist hedge fund Trian Partners disclosed a huge stake in the fast-food company and plans for a possible sale.

In a Securities and Exchange Commission filing late Tuesday, Trian disclosed a 19.4% stake in Wendy’s WEN, -2.34% and said it had advised the board it intends “to explore and evaluate the possibility” of a “potential transaction with respect to the company to enhance shareholder value.”

Wendy’s shares surged 15% after hours, following a 2.3% decline to close the regular session at $16.27. At Tuesday’s close, shares are down 30% over the past 12 months, while the S&P 500 index SPX, -0.81% is off 6.1%.

”Such a potential transaction could include an acquisition, business combination (such as a merger, consolidation, tender offer or similar transaction) or other transaction that would result in the acquisition of control of the company by the filing persons and/or their affiliates,” according to the filing.

Of the 41.2 million shares owned by Trian, Peltz directly owns nearly 10 million shares, while Trian founding partner and President Peter May directly owns 5.5 million shares.