His son's rape of Lucretia led to his expulsion and subsequent alliance with Lars Porsenna.
According to Livy, this ruler cut off the heads of the tallest poppies while talking to a messenger in a garden, which allowed his son to know how to conquer Gabii. This ruler allied with Aristodemus of Cumae and Octavius Mamillus, and he sought the help of the king of Clusium. This ruler purchased only three of the original nine (*) Sibylline Books, and his son Aruns killed Lucius Iunius Brutus in battle. His son's rape of Lucretia led to his expulsion and subsequent alliance with Lars Porsenna. For 10 points, identify this figure driven from Rome in 510 B.C., the seventh and last king of Rome. 
According to Livy, this ruler cut off the heads of the tallest poppies while talking to a messenger in a garden, which allowed his son to know how to conquer Gabii.
Tarquinius Superbus [accept Tarquinius the Proud, do NOT accept or prompt on "Tarquinius Priscus"]