She is the mother of King Alfred the Great. Her father, named Oslac, once served King Ethelwulf as the royal cup-bearer (the king later marrying Osburgh). Ethelwulf and Osburgh are 29X great-grandparents of Marie Antoinette:
AEthelwulf, King of Wessex=Osburgh

Alfred "The Great," King of Wessex=
Ealhswith of Mercia

Edward "The Elder," King of the Anglo-Saxons=
Edgiva

Edmund I, King of the English=Elgiva
Edgar I "The Peaceful," King of England=Elfrida

Ethelred II "the Unready," King of England=
Alfflaed

Edmund II "Ironside," King of England=unknown
Edward Aetheling=unknown

St. Margaret of Scotland=
Malcolm III, King of Scots

Maud of Scotland=
Henry I "Beauclerc," King of England

Maud of England=Geoffrey Plantagenet
Henry II, King of England=Eleanor of Aquitaine
John, King of England=Isabelle of Angouleme
Henry III, King of England=Eleanor of Provence
Edward I, King of England=Eleanor of Castile
Edward II, King of England=Isabella of France

Edward III, King of England=
Philippa of Hainault

John of Gaunt=Katherine Roet
John Beaufort=Margaret Holland
Joan Beaufort=James I, King of Scotland
James II, King of Scotland=Mary of Guelders

James III, King of Scotland=
Margaret Oldenburg

James IV, King of Scotland=Margaret Tudor
James V, King of Scotland=Mary of Guise
Mary, Queen of Scots=Sir Henry Stuart
James I, King of England=Anne of Denmark
Elizabeth of England=Friedrich V of Pfalz

Karl I Ludwig of Pfalz=
Charlotte of Hessen-Kassel

Elisabeth of Pfalz=
Philippe I Duke of Bourbon-Orleans

Elisabeth of Orleans-Chartres=
Duke Leopold of Lothringen-Teschen

Francis I, Emperor of the Holy Roman Empire=
Maria Theresa of Austria

Marie Antoinette=Louis XVI, King of France

Divorced in A.D. 853, Osburgh died sometime after 876. Source: Weis, F.L., (line 1 in) Ancestral Roots of Certain American Colonists . . .(2004).