1. The bodies of Romeo and Juliet. When the Prince and the other characters arrive at the Capulet tomb, they find the bodies of Romeo and Juliet. This is strong evidence that they are both dead, as Friar Laurence claimed.
2. Friar Laurence's confession. After the bodies of Romeo and Juliet are found, Friar Laurence confesses that he married them. This is also strong evidence that Friar Laurence's tale is true, as he would have no reason to lie about something that could get him in trouble.