First, as noted, he left in 2013. Second, according to this
Forbes article, his stake was less than five percent. The term "owns" generally implies a controlling interest.
Sunak left TCIF in 2009 to join Santa Monica-based Theleme Partners, a fund set up by former TCIF cofounder Patrick Degorce. Sunak owned less than 5% of the firm, which had $2.2 billion in assets under management according to the last available disclosure form filed in February 2013. He left Theleme in 2013 to launch Catamaran Ventures UK with his wife, Akshata.
In fairness, I observe that the article also states that Sunak and his wife cofounded Catamaran; I'd read earlier that her father owned the company. However, she has announced that Catamaran will be winding down its operations this year.
ETA: Reading further, I see that they founded Caramaran UK, a subsidiary of Catamaran, which is owned by her father.