Swietoslawa, * 967/972, + ca. 1016, was first married to Erik Sejersæl ( Eric the Victorious) of Sweden and was the mother of Olof Skötkonung; later married to Svend Tveskæg, (Sweyn Forkbeard), king of Denmark. From her second marriage she was probably the mother of Harald and Knud den Store (Canute the Great), king of Denmark, Norway and England. Sigrid Storråde's name is only mentioned in the sagas, while Gunhild was the name she got when she came to the North.
Several contemporary chronicles say that Harald 2. and Knud den Store had a Slavic mother, either from Poland or a neighbouring area. This supports the theory that Sigrid was a daughter of Mieszko 1. of Poland, although it is not ruled out that another person got the name Gunhild. The name Sigrid was interpreted as a distortion of the Polish name Swietoslawa, and the majority of Polish historians consider Sigrid and Swietoslawa the same person - and Sigrid of the Sagas as fictional. A possible explanation - that there are two variants of the same woman Svend Tveskæg married - is that he was married twice, and that Adam of Bremen did not know. This means that Olof Skötkonung and Knud den Store were made halfbrothers by a mnisunderstanding.
Thietmar of Merseburg is usually considered the best informed of the medieval chronicle writers, since he was contemporary to the events and very knowledgeable about the relations both in Denmark and Poland. He also mentions a Wendic Gunhild, but he does not say that the Wendic princess Gunhild was earlier married to the Swedish king. He writes that Mieszko 1.'s daughter and Boleslaw 1.'s sister married Svend Tveskæg and that she gave him two sons, Knud and Harald, but does not mention her name in this connexion.
Adam of Bremen claimed that Olof Skötkonung and Knud den Store were sons of an unnamed Wendic princess. In a later edition to this she appears to be named Gunhild. Adam writes that a Polish princess was the wife of Erik Sejersæl, and that she was the mother of Knud den Store and Harald 2.
It has i.e.been suggested that a Slavic princess was the mother of Olof Skötkonung and that she later married Svend Tveskæg. If she is identical to Sigrid Storråde this cannot be proved. It has led to speculations if there in reality were to different women. One, a Christian Slavic princess and another, a heathen Swedish magnate's daughter. The informations in the late Nordic sources differ in several points from the contemporary chronicles, which point out that Sigrid was of Slavic origin.
Gesta Cnutonis regis mentions in a short passage that Knud and his brother went together to Slavia to fetch their mother, who lived there.(after Svend's death). This does not necessarily mean that she was of Slavic origin, although it is very probable. The assumption that Harald and Knud's mother was the sister of Boleslaw 1. explains some of the enigmatic informations from several chronicles that i.e. Polish troups participated in Knud's invasion of England. The hypothesis that Swietoslawa changed her name twice seems unlikely.
Liber vitae from New Minster and Hyde Abbey in Winchester has a text which says that Knud den Store's sister was named "Santslaue" ("Santslaue soror CNVTI regis nostri"),which without doubt is a slavic name. She might probably was probably named after her mother Świętosława.
(Note: I don't think Santslaue is similar to Swietoslawa)
From a new article by Jagoda Urban-Klaehn: (from Norman Davis' book: God's Playground. A History of Poland):
After 994 she married Sweyn I of Denmark under the name Gunhilda. (He says like the Polish historians that she was first married to Erik Sejersæl under the name Sigrid). From the second marriage she probably had five children, including Canute the Great and Harold II. Since her marriage was not happy, she returned to Poland, where her brother Boleslaw the Brave was ruling. After Sweyn died, her sons Canute and Harald took her back from Poland. She died somewhere in an English castle. In any event, Boleslaw I of Poland actually sent his troops to help Canute in his successful conquest of England, another sign of close relationships between Polish rulers and Vikings.
It is said that Swietoslawa's difficult character was inherited after her aunt Adelaide (Polish Adelajda), who was probably a sister of Mieszko I and also the wife of the Hungarian duke Geza. Adelaide became a mother of St. Stephen the Great (977-1038) who became the first king of Hungary and a saint. Adelaide was known as a beauty, but she drunk excessively and loved riding horses like a man. Once, she even killed a man in a rage. (Very much like the legendary Sigrid Storråde)!
An almost new one:
British Foreign Secretary David Miliband delivered on 23 June 2009 a speech during his first visit to the country as foreign secretary in Warsaw, Poland. He argued that Europe's creation and evolution represent one of the most visionary acts of statesmanship of the 20th century and the start of his speech was like this: "Any British Foreign Secretary visiting Poland is deeply conscious of the history between our two countries. It goes back a long way. Canute the half Polish King of Denmark who, in 1015, invaded England, bringing with him Polish soldiers and his mother, Princess Swietoslawa, who was buried in Winchester castle. [...]
If you search for burials in Winchester cathedral, Swietoslawa is not there.
A Polish website/Prominent Polish Women says: Swietoslawa died after 2/2/1014, in Kamien Pomorski, Poland