Found: One Secret Baby (UK)

Uncovering her secret...

LA lawyer Rosalie Walker will do whatever it takes to protect her adopted son. She promised his mother before she died that she'd look after him and keep him safe from his paternal family. So when delectable Morgan Danby walks into her office in search of his nephew, she must keep the baby in her care a secret--even if one look from Morgan makes her want to share everything with him...

As a favour to his step-mother-- the woman who actually raised him, unlike his real mother who abandoned him as a child--successful businessman, Morgan is searching for the son of his incarcerated step-brother. He can tell Rosalie is hiding something and the temptation to seduce her for her secret is strong, but will he be able to handle the consequences once all is revealed...?