The ENQUIRER exclusively reveals Lindsay Lohan is going to have a new stepmum!

Her dad Michael recently popped the question to 34-year-old GF Erin Muller, a missionary worker.

"Erin happily said yes and is now sporting a gorgeous 31/2-carat diamond," an insider told The ENQUIRER.

The engagement is much-needed good news for Big Mike, 48, who was recently hit with a paternity claim from a former lover in Montana.

 Kristi Kaufmann, with whom Michael had an affair in 1995, claims he is the father of her 13-year-old daughter.

For all the details pick up The ENQUIRER on sale now!