No King Stephen

When King Henry I of England died in 1135, Stephen of Blois, with the help of his brother Henry of Blois, took the throne. Stephen argued that the preservation of order across the kingdom took priority over his earlier oaths to support the claim of Henry's daughter, the Empress Matilda.

Suppose Stephen of Blois dies in 1134. What happens then?
Does Stephen's eldest son, Eustace of Boulogne become King Eustace I?
 
Remember when you said this?
Stephen argued that the preservation of order across the kingdom took priority

Exactly what aspect of a five-year-old kid somehow seizing the throne in contravention of the established law of succession would preserve order? The nobles of England had already sworn an oath to accept Matilda as her father's successor, and the only reason half of them abandoned their oaths was that Stephen was an adult man and got to England first. In no way would Eustace be a credible rival to Matilda in 1135. In fact, because her bastard brothers were loyal to her, the only rival would be Theobald, who (importantly) didn't make it in time IOTL. That means that he's got to be far more tenacious than his brother in order to gain and keep the throne.
 
No way. Theobald of Champagne invades and faces a Matilda with more significant native support.

Indeed Stephen was the 3rd son of Stephen II Henry, Count of Champagne & Blois.
The first being William, Count of Sully, who was passed over as Count of Blois due to his "erratic" behaviour (he was possibly mad or deranged in some way).
The second being Theobald, Count of Champagne & Blois.
The fourth being Henry who became Bishop of Winchester and was Stephen's ally for the throne.
 
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