This article deals with a now lost runestone, which previously was known only from an unconvincing drawing from the 18th century, and therefore never accepted as genuine in the corpus edition Upplands runinskrifter. Some overlooked material in the archives show, however, that it was in fact a genuine runestone dating to the late Viking Age. It is also evident that the runestone fragment U520, which Richard Dybeck found at the settlement Björkholmen in 1870, originally formed a part of this stone. According to the fragmentary text the stone was erected by at least two brothers, Ingvarr and possibly Anundr, in memory oftheir father. This combination of names indicates that the stone was commissioned by the same magnate family known from a couple of runestones in the vicinity (U 513 and U 540) and which by some researchers have been connected to the Viking Age chieftain Ingvar the Far-Travelled. This connection is rejected by the present author, who suggests instead that another member of the same family might have played a role in some events in Swedish history after the death of king Stenkil in 1066.