Mr Foster’s wife Katharine McPhee attended the same school as Meghan where she grew up in California.
However, Prince Harry’s relatives will not be present at the lavish party, and neither will Thomas Markle, Meghan’s estranged father.
Speaking to the Sunday Mirror, a source said: “David wants to make him special to Harry but also to keep him laid back and low-key with good wine, good food and intimate company.
“He sets aside the home at his home as well as all the outdoor space, which security will seal off.
“The small gathering will also include his daughters Erin and Sara and their husbands.
“They are about the same age as Harry and Meghan.
“David helped connect the Sussexes so they could form a close group of friends and feel more comfortable in Los Angeles.”
READ MORE: France quarantine: Boris Johnson warned to prepare for a violent reaction
Ms PcPhee said her husband has a big heart and “loves helping those he loves”.
She added: “Meghan and I have known each other since childhood but Harry and my husband are really friends. It’s good. “
The Duchess recently celebrated her 39th birthday in a private celebration with Harry.
For the special day, Prince Harry is said to have prepared a three-course dinner for Meghan Markle while Doria babysits Archie.
A source close to the family said: ‘They spent the day with the family and in the evening Doria looked after Archie so that Meghan and Harry could spend time as a couple.