A young Manchester United fan was left speechless after he had a chance encounter with Kobbie Mainoo’s father and ‘famous’ brother at the FA Cup final on Saturday. Kobbie Mainoo played a starring role for Manchester United and the England midfielder produced a show-stealing performance at Wembley. Alejandro Garnacho opened the scoring in the first half before Mainoo doubled United’s advantage over Manchester City before half-time. Jeremy Doku pulled one back for Manchester City late in the second half, but Pep Guardiola’s men were outclassed by United in the FA Cup final. Mainoo had a remarkab…