Pete Wentz traditionally asked Ashlee Simpson's father Joe for her hand in marriage.
The couple was on a trip to Colorado when the Fall Out Boy bassist, 28, asked Simpson - his girlfriend of almost two years - to marry him.
But Simpson's father Joe already knew about his plans to propose.
He tells People.com, "(Pete) did ask me. I told him that I would be honoured to have him as part of my family."
Meanwhile, Simpson's older sister Jessica has spoke about her happiness for the couple.
She says, "My sister is overflowing with joy. Pete is an incredible soul. They naturally bring out the best in each other. I couldn't be happier."