He had been with the wrong mother.
Jim Weber’s database has:
Peter de Leigh was born ABT 1300 in Knutsford Booths Hall, Bucklow, Cheshire, England, and died Deceased in Betchton, Congleton, Cheshire, England. He married Ellen de Bechton. He was the son of John de Legh and Ellen Dent.
https://wc.rootsweb.com/trees/162642/I05696/peterde-leigh/individual
I’ve uploaded the page and adjusted the family accordingly. His rootsweb database is good on this area of English history, but of course you should look at the scholarly source data yourself.
Because of Omerod, who I think later corrects himself.
From Nancy Lopez
In _George Ormerod's The History of County Palatine and City of Chester_, Vol. I, p.499, Vol. III, p. 661, John Legh is only shown as married to one Ellen, Ellen Coroun (Corona), sister of John Coronun & daughter of Thomas Corona, lords of Adelynton. She was living 1296, Inq.p.m. 26 Edward III. All of John's sons are credited to Ellen Corona, including John, who is given as the second son. Robert is shown as the eldest son and heir to Addlington. John is heir to Booths. Copied from "Leigh and Legh of High Legh" website, www.users.totalise.co.uk: