Diana, 70, is excited that Evan will tie the knot with Ashlee Simpson, at her mansion in Los Angeles, reported Contactmusic.
"Diana couldn't be more excited for her son Evan to marry Ashlee. She offered them her LA home as the venue, and she's been renovating it for the occasion," a source said.
The couple are planning to pull out all the stops for their luxurious celebration in August.
"It's going to be so over-the-top," the source added.
The singer is also expected to sing for the guests at the reception accompanied by daughter Rhonda Ross Kendrick.