Arthur Donald – Paul McCartney’s Grandson If you feel like you’ve seen Yale undergrad Arthur Donald before, one look at an old picture of his granddad should clear things out for you. Donald is Sir Paul McCartney’s eldest grandchild through the former Beatle’s daughter Mary. Judging by Sir Paul’s monstrous net worth (estimated to be at $1.1 billion in the year 2018), Arthur doesn’t seem like the kind who will have any problems paying the steep tuition at Yale.