Complex sentence: John was his son by his first wife, born about 1290, and was knighted, as was his father, with Edward, Prince of Wales, on 12 May 1306.
Split into simpler sentences: John was his son by his first wife. John Maltravers the younger was born about 1290, and was knighted, as was his father, with Edward, Prince of Wales, on 12 May 1306.