The Peabody Essex Museum has announced it’s ending its relationship with Rick Mather Architects following Mather’s death in April from a heart attack. The firm, renowned for its work on the Ashmolean Museum at the University of Oxford and the Dulwich Picture Gallery in London, had been designing PEM’s 175,000-square-foot expansion. “We are deeply saddened by Rick Mather’s passing. It was a privilege and an honor to work with Rick and his team. He was a gifted architect,” Dan Monroe, PEM’s Rose-Marie and Eijk van Otterloo director and CEO, said in a statement. “After careful consideration, we have determined the best way forward to complete our expansion project is to engage the services of another firm for the next phase of design.” No word on who might take over, but it’s worth noting that Moshe Safdie was the architect of PEM’s last expansion.