The Beady Eye star, 40, will attend the annual gardening event on the same day as the Queen, The Sun reports.
It said that the ex-Oasis frontman had requested tickets for a VIP preview day of the famous show, which celebrates its 100th anniversary this year.
A source said: "Liam is one of the most unlikely guests in the event's history.
"His rampaging days are definitely over - which is a relief to organisers given the importance of some of the guests."
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