https://en.wikipedia.org/wiki/Gilbert,_Duke_of_Lorraine

Gilbert was the duke of Lotharingia until 939.

The beginning of the reign of Gilbert is not clear. A dux Lotharingiae is mentioned in 910 and this may have been Gilbert. Lotharingia sided with Charles III in 911, who was deposed in West Francia in 922 by Robert but remained king in Lotharingia, from where he tried to reconquer West Francia until being imprisoned in 923.

In 925, Gilbert swore fealty to King Henry the Fowler of Germany as duke of Lotharingia. Gilbert married Henry's daughter Gerberga of Saxony by 930. For whatever reason, Gilbert rebelled when Henry died in 936 and changed allegiance to Louis IV of France, where the king had less authority. Gilbert managed to be practically independent for three years until he was defeated by the army of king Otto I of Germany in 939 at the Battle of Andernach. Gilbert was made prisoner, and succeeded in fleeing but drowned while trying to cross the Rhine. Lorraine was given to Henry I, Duke of Bavaria.