The official website for the OVA Code Geass Lelouch of the Rebellion: Nunnally in Wonderland has updated to announce the full details of the OVA release. The approximately 30 minute OVA will be released on July 27th on Blu-ray and DVD in Japan.

The Blu-ray has an MSRP of 4200 yen (~$52 USD) while the DVD will go for 3675 yen (~$45 USD). Both come with optional English subtitles and include the 40 page full color A4 size picture book.
The OVA is directed by Baba Makoto with a scenario by R2's Yuuichi Nomura.
The OVA tells another story of Alice in Wonderland when, while spending time with his sister one sunny day, Nunnally requests that Lelouch tells a story, like in old times. To grant his sister's request, Lelouch uses Geass on the entire cast of the Code Geass series:
I, Lelouch Vi Britannia command you! Characters of Code Geass, become characters in my story and entertain my beloved Nunnally.
Thus with the biggest waste of Geass in Code Geass history, a new story of Alice in Wonderland takes place.
via Yaraon!
Image ©SUNRISE/PROJECT GEASS・MBS Character Design ©Clamp
Updated: Added plot