Fold whipped cream into pastry cream and you get diplomat cream. I don't know how this pastry filling got its name, but I can tell you that if you arm yourself with some diplomat cream all conflicts would melt away because everyone would be too busy swooning and licking their fingers. It's one of those fabulous kitchen marriages where the whole is greater than the sum of its parts.
Use it to fill cream puffs, eclairs, fresh fruit tarts, brioche style cakes, or just layer if with fresh fruit and leftover cake for a beautiful trifle.
Important: Don't reuse the bowl or whisk after whipping cream to whip your pastry cream! I once made that mistake and the remaining whipped cream that was clinging to the bowl and whisk turned to butter and made the pastry cream grainy.
Fold about one third of the whipped cream into the pastry cream to lighten it. Then fold the rest of the whipped cream in. The proportions are not set in stone. You can adjust the ratio of whipped cream to pastry cream to your liking and application. Use immediately or store in the fridge. Best if used the day it's made. It will start to thin out after sitting in the fridge for more than 24 hours.