Bill Ackman has a big, new investment that he doesn’t want anyone to know about — yet.

Ackman teased the new position, which accounts for roughly 10 percent of his Pershing Square hedge fund’s portfolio, in a call with investors Wednesday.

“We’re not yet ready to disclose the company, but it certainly meets our standards,” Ackman said, noting that the mystery investment is “quite undervalued” and has “lots of opportunity for improvement.”

Ackman could use some upside.

Although his fund is up 13.6 percent this year, it’s coming off a low base. Assets stand at roughly $8 billion, down from a peak of $20 billion in July 2015, slammed by a disastrous bet on scandal-plagued pharma giant Valeant and an ill-fated, $1 billion short position on Herbalife.

Fleeing investors forced Pershing Square to sell down some of its winning position in Automatic Data Processing, Ackman said.

We “are not saying we don’t like the investment. In fact, we like it a lot, but we do need to manage the portfolio overall,” he said.

ADP shares are up nearly 27 percent since Pershing Square revealed its stake in the company via regulatory filings last August. Ackman was unsuccessful in winning seats on the board in November but said he is “pleased” with his conversations with management since then.