Here's a bit of history of the site from the English Heritage website:-
The Franciscan friary at Gloucester was founded in 1231, but in about 1518 a prominent local family, the Berkeleys of Berkeley Castle, paid for the church to be rebuilt in Perpendicular Gothic style. This incorporated the earlier church but only survived a short while as the friary was surrendered to the king in 1539 at the suppression of the monasteries.
Over the following years, the buildings were put to a number of different uses and in 1643 they were severely damaged by Royalist forces during the siege of Gloucester.
By 1721 only the nave and its north aisle survived and later in the 18th century houses were built within the walls. In 1810 a large house was built into the west end of the medieval remains and this is now a public library.