According to the current construction of this tree, she and her husband Thomas de Mumby de Willoughby are HALF-SIBLINGS who had *the same mother*!!!!!!
This has never been legal, moral or allowed in *any* Western European country at *any* time.
It seems likely that an Alice Nn who married William de Mumby was misparented and/or mismerged onto the Willoughby tree. This is specially likely because Alice de Beke was married to and having children with Sir William de Willoughby at the same time that Alice Nn was bearing Margaret to William de Mumby.
William de WILLOUGHBY
Born about 1245 - probablement Willoughby, Lincolnshire
Deceased about 1295
Parents
Robert de WILLOUGHBY ca 1217-/1256
Alice Margaret De ORREBY ca 1221-
Spouses and children
Married to Alice BEKE, Heiress of Eresby ca 1250-1311/
(Parents : John BEKE, Baron of Eresby ca 1223-1303/1304 & Sarah FURNIVALL ca 1220-) with
M Thomas WILLOUGHBY 1268- married to Margaret De MUMBY ca 1270-
M Robert WILLOUGHBY, 1st Baron of Eresby ca 1271-/1317 married about 1303 to Margaret DEINCOURT ca 1275-/133
ttps://gw.geneanet.org/lard?lang=en&pz=jean+charles&nz=terlinden&ocz=0&p=william&n=de+willoughby&oc=1
Thomas WILLOUGHBY
Born in 1268
Deceased
Parents
William de WILLOUGHBY, knight ca 1245-ca 1295
Alice BEKE, Heiress of Eresby ca 1250-1311/
Spouses and children
Married to Margaret De MUMBY ca 1270- (Parents : William De MUMBY ca 1240- & ? ?) with
F Agnes WILLOUGHBY ca 1275- married to William De HILTOFT ca 1275-
https://gw.geneanet.org/lard?lang=en&pz=jean+charles&nz=ter...
Margaret De MUMBY
Born about 1270
Deceased
Parents
William De MUMBY ca 1240-
? ?
Spouses and children
Married to Thomas WILLOUGHBY 1268- (Parents : William de WILLOUGHBY, knight ca 1245-ca 1295 & Alice BEKE, Heiress of Eresby ca 1250-1311/) with
F Agnes WILLOUGHBY ca 1275- married to William De HILTOFT ca 1275-
https://gw.geneanet.org/lard?lang=en&pz=jean+charles&nz=ter...
William De MUMBY2
Born about 1240
Deceased
Spouses and children
Married to ? ? with
F Margaret De MUMBY ca 1270- married to Thomas WILLOUGHBY 12
https://gw.geneanet.org/lard?lang=en&pz=jean+charles&nz=ter...
William de Mumby
Birth abt 1240 England, Lincolnshire, Spilsby, Mumby
Children First Name Birth Dt Death Dt Birth Place
Margaret de Mumby
abt 1270 England, Lincolnshire, Spilsby, Mumby
Spouse Thomas de Willoughby
https://www.ourfamtree.org/browse.php/William-de-Mumby/f9532