The Duke's Shotgun Wedding

The Duke's Shotgun Wedding tells the story of Jocelyn, a lady who shows up with a pistol in Duke Sebastian's office demanding he force his brother to marry her.

She does this because his brother compromised her.

Sebastian has recently discovered his siblings are not his father's children and feels he must have an heir so he marries her himself.

Jocelyn helps him restore his family.

The story is an example of forced marriage trope with a great bang at the beginning.