What was the name of Ada Lovelace's half-sister, Lord Byron's illegitimate daughter?

Ada Lovelace’s half-sister, Lord Byron’s illegitimate daughter, was Allegra Byron.

Allegra was born Alba Byron in Bath in January 1817 to the poet George Gordon, Lord Byron, and Claire Clairmont. Byron later changed her name to Allegra, an Italian word associated with liveliness or cheerfulness. She was born shortly after Byron left England and became part of the complicated network surrounding Byron, the Shelleys, and Claire Clairmont.

When Allegra was about fifteen months old, Claire handed her over to Byron. He placed the child with foster families and eventually sent her to a Roman Catholic convent in Italy. Byron asked his half-sister Augusta Leigh to take Allegra into her household, but Leigh refused.

Allegra died in Italy in April 1822 at about five years old, probably from typhus or malaria. Ada Lovelace never met her younger half-sister. Readers sometimes confuse Allegra with Elizabeth Medora Leigh, another girl whom Lady Byron believed might have been Byron’s daughter, but Medora’s parentage remained disputed. Allegra is the clearly documented illegitimate daughter of Byron and Claire Clairmont.