The late comedian's memorial service is slated to go down June 23 at the Roosevelt Hotel's ballroom. We're told Tiffany and actress Marla Gibbs have confirmed they'll attend.
As for the former 'Late Night' host, we're told Letterman -- along with the Angela & John Witherspoon Foundation -- are just some of the peeps who have contributed toward the cost of the memorial service.
Actor Tim Reid ... along with comedian J. Anthony Brown and Richard and Tina Lawson have also contributed to cover costs.
Chris Tucker and George Wallace are some of the comedians who can't attend the service, but instead will send a video tribute. We're also told invitations have been extended to Eddie Murphy and Dave Chappelle.