Sir Thomas Barrett-Lennard, 1st Baronet

https://en.wikipedia.org/wiki/Sir_Thomas_Barrett-Lennard,_1st_Baronet

Sir Thomas Barrett-Lennard, 1st Baronet FSA, DL (6 January 1761 – 25 June 1857) was a British politician and baronet.

https://www.wikitree.com/wiki/Barrett-Lennard-4

Sir Thomas Barrett-Lennard, 1st Bt. was born illegitimately on 6 January 1762. Lord Dacre had a son out of marriage by Elizabeth FitzThomas; Thomas, later 1st Baronet, was born in 1762 and was brought up by Lord and Lady Dacre and treated as if he had been the legitimate offspring of their marriage. Anna Maria acted as a mother, and as an exceptionally good mother too. Knowing she could have no more children, she connived at this intrigue for her husband's sake as he was anxious to have a son to whom he might leave the family estates.

The boy was given the education and upbringing that would prepare him to assume the rank and status of the Barrett Lennard family. Lord Dacre died in 1786 and in his will he asked his wife to 'take upon herself the guardianship of his child, who he directed was to assume the names of Barrett and Lennard and the arms and crests belonging to those families'. This she did."

http://www.historyofparliamentonline.org/volume/1820-1832/member/ba...