Jean IV de Brosse was the son of René de Brosse

René de Brosse

René de Brosse, also René de Bretagne was the elder son of Jean II de Brosse. He was killed at the Battle of Pavia on 24 February 1524.He was the father of Jean IV de Brosse.-Notes:...

 and Jeanne de Commines (daughter of Philippe de Commines

Philippe de Commines

Philippe de Commines was a writer and diplomat in the courts of Burgundy and France. He has been called "the first truly modern writer" and "the first critical and philosophical historian since classical times"...

).

After the death of his father at the Battle of Pavia

Battle of Pavia

The Battle of Pavia, fought on the morning of 24 February 1525, was the decisive engagement of the Italian War of 1521–26.A Spanish-Imperial army under the nominal command of Charles de Lannoy attacked the French army under the personal command of Francis I of France in the great hunting preserve...

, he succeeded him as Count of Penthièvre.

In 1533, he married Anne de Pisseleu d'Heilly

Anne de Pisseleu d'Heilly

Anne de Pisseleu d'Heilly , Duchess of Étampes, was the mistress of Francis I of France.She was a daughter of Adrien de Pisseleu, seigneur d'Heilly, a nobleman of Picardy, who, with the rise of his daughter at court, was made seigneur of Meudon, master of waters and forests of Île de France, of...

, the mistress of Francis I of France

Francis I of France

Francis I was King of France from 1515 until his death. During his reign, huge cultural changes took place in France and he has been called France's original Renaissance monarch...

, and was shortly thereafter created count, then duke of Étampes. However, he was greatly impoverished by the expenditures necessary to maintain their position at court. With the death of Francis I, the antipathy of Diane de Poitiers

Diane de Poitiers

Diane de Poitiers was a French noblewoman and a prominent courtier at the courts of kings Francis I and his son, Henry II of France. She became notorious as the latter's favourite mistress...

 compelled Jean to retreat to Brittany

Brittany

Brittany is a cultural and administrative region in the north-west of France. Previously a kingdom and then a duchy, Brittany was united to the Kingdom of France in 1532 as a province. Brittany has also been referred to as Less, Lesser or Little Britain...

, where he had been appointed governor in 1543; she also obtained his duchy of Étampes. After the death of Henry II of France

Henry II of France

Henry II was King of France from 31 March 1547 until his death in 1559.-Early years:Henry was born in the royal Château de Saint-Germain-en-Laye, near Paris, the son of Francis I and Claude, Duchess of Brittany .His father was captured at the Battle of Pavia in 1525 by his sworn enemy,...

 and the fall of Diane, he was able to regain the duchy, but died not long thereafter.