https://wikipedia.tel/%D0%95%D0%B2%D0%BD%D0%B0_%D0%9F%D0%BE%D0%BB%D...
And there is explanation that he was not first son of Gedymin (so and mother must be not some Vida of Courland but Evna of Polock):
https://wikipedia.tel/%D0%9C%D0%BE%D0%BD%D1%82%D0%B2%D0%B8%D0%B4