apologetic (adj)

The boy felt apologetic after losing his sister’s favorite toy.
After realizing he had mistakenly taken her umbrella, he was quick to send an apologetic text and promised to return it the next day.
Her apologetic tone and sincere apology helped mend the strained relationship with her friend, who had felt hurt by their previous argument.
The employee was genuinely apologetic for the error in the report and took full responsibility for the mistake, promising to rectify it promptly.