'Harry Potter' Reunion Trailer: Emma Watson Tears Up Reuniting With Co-Stars

 Daniel Radcliffe, Emma Watson, Rupert Grint and their castmates are seen all together in the first trailer for ‘Harry Potter 20th Anniversary: Return to Hogwarts.’ The highly-anticipated retrospective features appearances from Tom Felton, Helena Bonham Carter, Gary Oldman, Ralph Fiennes and more familiar faces from the franchise. ET chats with Rupert, who plays Ron Weasley, who explains why the reunion was so emotional. ‘Harry Potter 20th Anniversary: Return to Hogwarts’ premieres Jan. 1 on HBO Max.