Ada, sister and coheir of John the Scot, 10th Earl of Huntingdon, 3rd daughter of David of Scotland, 9th Earl of Huntingdon. [Complete Peerage VI:345]
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on the history of the Earldom of Huntingdon:
After Earl Simon's [Matilda's 1st husband] death, his Widow married David I of Scotland, who consequently became Earl of Huntingdon too, keeping the Earldom even after he succeeded his brother as King of Scots. He sided with the Empress Maud against Stephen I but came to terms with the latter and made the Earldom over to his son Henry. Henry swore fealty to Stephen but subsequently fought against him under the Scottish banner, which may account for Simon de St Liz's son, another Simon, being recognized as Earl of Huntingdon before Henry's death in 1152. Thereafter the Earldom was more or less bounced back and forth between the de St Liz family and the Kings of Scotland, first being held 1157-65 by Malcolm the Maiden and (1165-74) by his brother William The Lion, King of Scots, then by a Simon de St Liz (grandson of the first Simon and son of the second) from 1174 to 1184.
When the third Simon de St Liz died in 1184 he left no surviving issue and David, younger brother of the Kings of Scots just mentioned, assumed the Earldom from 1185 (on the handing over of it to him by William the Lion) till it was taken away from him in 1215 or 1216 by King John. He got it back again in 1218, however. It is this David's daughter who married Sir Henry de Hastinges, ancestor of the Lords (Barons) Hastings of which the current Hastings holdersof the Huntingdon Earldom are cadets....A little over a century later the then Lord Clinton was promoted Earl of Huntingdon. Apart from his wife being the widow of Lord Hastings he seems to have had no family connection with the title's previous holders. [Burke's Peerage]