From the memorandum book of Rev. John Sparhawk: "My dear and only brother, Nath'l, was married at Kittery to Miss Elizabeth Pepperrell, the only daughter of the then Hon'ble William Pepperrell, Esq., now Sir William Pepperrell, Bart., on June 10, 1742."
[Note: A letter from the Duke of Newcastle dated 10 Aug 1745 informing William Pepperell that he was a Baronet, was received 23 Sep 1745 (see here), so this was written sometime after that date.]