This profile for Sir Thomas de Grey seems to have been miss-merged at sometime. It must of been near Jan 6, 2014 at 7:27 PM as this is when the parents John & Lucy were removed and to far back for a undo merge, but I'm not sure this John Grey, of Heaton & Lucy de Mohun would be Thomas' correct parents.
His dates look to be for Thomas son of John de Grey and father of Thomas de Grey who married Agnes de Beyle, Robert & Joan but probably not the one who married Guy le Bretton.
The Thomas de Grey who is son of Sir Robert de Grey, kt. and Joan de Valoines, had dau. Joan de Grey who married m. Guy le Bretton.
I have not seen the wives of either Thomas de Grey on the references.
There is a Thomas de Grey who married a Alice Neville, son of Sir Thomas Grey, Kt., of Heaton and Joan (Jane) de Mowbray but he was born in 1384, the Alice Neville connected as wife to this Sir Thomas is listed born circa 1269.