With occupancy of the 201,998-square-foot converted mill complex at 98 percent, Spear Street Capital has sold Riverworks at Aetna Mills in Watertown to Boston-based Paradigm Properties.

San Francisco-based Spear Street paid $43 million for the three-building complex at 480 Pleasant St. in June 2014 and cashed out for $63.8 million on Oct. 16.

Originally built in 1907, the former woolen mill was converted into office space including Boston Scientific’s former headquarters. In recent years, owners have operated the complex as a multitenant property and updated common areas, building systems and an interior courtyard.

“With the building 98 percent leased to 15 tenants with staggered lease expirations, we are focused on further activating Riverworks through our client-focused property management services and managing for long-term appreciation as Watertown continues its ascent for a wide range of companies,” Paradigm President John Caldwell said in a statement.